TWU Informer, you have the graph correct, but seemingly in an attempt to deceive, you edited the text.
Attached is the full and complete text found from
http://en.wikipedia.org/wiki/Labor_unions_in_the_United_States
Possible causes of drop in membership

Rise and fall of union membership in the United States.
Although most
industrialized countries have seen a drop in unionization rates, the drop in union density (the unionized proportion of the working population) has been more significant in the United States than elsewhere. Dropping
unionization rates cannot be attributed entirely to changing
market structures. In fact, scholars have shown the tremendous complexity inherent in explaining the decline of union density.
Popularity

A historical comparison of union membership as a percentage of all workers and union support in the United States.
Public approval of unions climbed during the 1980s much as it did in other industrialized nations,[sup]
[18][/sup] but declined to below 50% for the first time in 2009 during the
Great Recession. It's not clear if this is a long term trend or a function of a high unemployment rate with historically correlates with lower public approval of labor unions.[sup]
[19][/sup] One explanation for loss of public support is simply the lack of union power or critical mass. No longer do a sizable percentage of American workers belonged to unions, or have family members who do. Unions no longer carry the “threat effect”. The power of unions to raise wages of non-union shops by virtue of the threat of unions to organize those shops.[sup]
[19][/sup]
Institutional environments
A broad range of forces have been identified as potential contributors to the drop in union density across countries. Sano and Williamson outline quantitative studies that assess the relevance of these factors across countries.[sup]
[20][/sup] The first relevant set of factors relate to the receptiveness of unions’ institutional environments. For example, the presence of a
Ghent system (where unions are responsible for the distribution of unemployment insurance) and of centralized collective bargaining (organized at a national or industry level as opposed to local or firm level) have both been shown to give unions more bargaining power and to correlate positively to higher rates of union density. Unions have enjoyed higher rates of success in locations where they have greater access to the workplace as an organizing space (as determined both by law and by employer acceptance), and where they benefit from a
corporatist relationship to the state and are thus allowed to participate more directly in the official governance structure. Moreover, the fluctuations of business cycles, particularly the rise and fall of unemployment rates and inflation, are also closely linked to changes in union density.[sup]
[20][/sup]
Legislation
Labor lawyer
Thomas Geoghegan attributes the drop to the long term effects of the 1947
Taft-Hartley Act, which slowed and then halted labor's growth and then, over many decades, enabled management to roll back its previous gains.[sup]
[21][/sup]
First, it ended organizing on the grand, 1930s scale. It outlawed mass picketing, secondary strikes of neutral employers, sit downs: in short, everything [Congress of Industrial Organizations founder John L.] Lewis did in the 1930s.
The second effect of Taft-Hartley was subtler and slower-working. It was to hold up any new organizing at all, even on a quiet, low-key scale. For example, Taft-Hartley ended "card checks." … Taft-Hartley required hearings, campaign periods, secret-ballot elections, and sometimes more hearings, before a union could be officially recognized.
It also allowed and even encouraged employers to threaten workers who want to organize. Employers could hold "captive meetings," bring workers into the office and chew them out for thinking about the Union.
And Taft-Hartley led to the "union-busting" that started in the late 1960s and continues today. It started when a new "profession" of labor consultants began to convince employers that they could violate the [pro-labor 1935] Wagner Act, fire workers at will, fire them deliberately for exercising their legal rights, and nothing would happen. The Wagner Act had never had any real sanctions.
[…]
So why hadn't employers been violating the Wagner Act all along? Well, at first, in the 1930s and 1940s, they tried, and they got riots in the streets: mass picketing, secondary strikes, etc. But after Taft-Hartley, unions couldn't retaliate like this, or they would end up with penalty fines and jail sentences.[sup]
[21][/sup]
In general the influence of politics in determining union strength in the US and other countries is contested. Brady[sup][
who?][/sup] writes that
political parties play an expected role in determining union strength, with
left-wing governments generally promoting greater union density, other scholars contest this finding by pointing out important counterexamples and explaining the reverse causality inherent in this relationship.[sup]
[22][/sup]
Globalization
More recently, as unions have become increasingly concerned with the impacts of market integration on their well-being, scholars have begun to assess whether popular concerns about a global “race to the bottom” are reflected in cross-country comparisons of union strength. These scholars use
foreign direct investment (FDI) and the size of a country’s international trade as a percentage of its
GDP to assess a country’s relative degree of market integration. These researchers typically find that
globalization does affect union density, but is dependent on other factors, such as unions’ access to the workplace and the centralization of bargaining.[sup]
[23][/sup] Sano and Williamson argue that globalization’s impact is conditional upon a country’s labor history.[sup]
[24][/sup] In the United States in particular, which has traditionally had relatively low levels of union density, globalization did not appear to significantly affect union density.
Employer strategies
Illegal union firing increased during the
Reagan administration and has continued since.[sup]
[25][/sup]
Studies focusing more narrowly on the U.S. labor movement corroborate the comparative findings about the importance of structural factors, but tend to emphasize the effects of changing labor markets due to globalization to a greater extent. Bronfenbrenner notes that changes in the economy, such as increased global competition,
capital flight, and the transitions from a
manufacturing to a
service economy and to a greater reliance on transitory and contingent workers, accounts for only a third of the decline in union density.[sup]
[26][/sup] She claims that the federal government in the 1980s was largely responsible for giving employers the perception that they could engage in aggressive strategies to repress the formation of unions. Richard Freeman also points to the role of repressive employer strategies in reducing unionization, and highlights the way in which a state ideology of anti-unionism tacitly accepted these strategies [sup]
[18][/sup] Goldfield notes that the overall effects of globalization on unionization in the particular case of the United States may be understated in
econometric studies on the subject.[sup]
[27][/sup] He writes that the threat of production shifts reduces unions’ bargaining power even if it does not eliminate them, and also claims that most of the effects of globalization on labor’s strength are indirect. They are most present in change towards a
neoliberal political context that has promoted the
deregulation and
privatization of some industries and accepted increased employer flexibility in labor markets.
Union responses to globalization
Studies done by Kate Bronfenbrenner at Cornell University show the adverse effects of globalization towards unions due to illegal threats of firing.[sup]
[28][/sup]
Regardless of the actual impact of market integration on union density or on workers themselves, organized labor has been engaged in a variety of strategies to limit the agenda of globalization and to promote labor regulations in an international context. The most prominent example of this has been the opposition of labor groups to free trade initiatives such as the North American Free Trade Agreement (NAFTA) and the Dominican Republic-Central American Free Trade Agreement (DR-CAFTA). In both cases, unions expressed strong opposition to the agreements, but to some extent pushed for the incorporation of basic labor standards in the agreement if one were to pass.[sup]
[29][/sup]
However, Mayer has written that it was precisely unions’ opposition to NAFTA overall that jeopardized organized labor’s ability to influence the debate on labor standards in a significant way.[sup]
[30][/sup] During Clinton’s presidential campaign, labor unions wanted NAFTA to include a side deal to provide for a kind of international social charter, a set of standards that would be enforceable both in domestic courts and through international institutions.
Mickey Kantor, then U.S. trade representative, had strong ties to organized labor and believed that he could get unions to come along with the agreement, particularly if they were given a strong voice in the negotiation process. However, when it became clear that Mexico would not stand for this kind of an agreement, some critics from the labor movement would not settle for any viable alternatives. In response, part of the labor movement wanted to declare their open opposition to the agreement, and to push for NAFTA’s rejection in Congress.[sup]
[30][/sup] Ultimately, the ambivalence of labor groups led those within the Administration who supported NAFTA to believe that strengthening NAFTA’s labor side agreement too much would cost more votes among Republicans than it would garner among Democrats, and would make it harder for the United States to elicit support from Mexico.[sup]
[31][/sup]
Graubart writes that, despite unions’ open disappointment with the outcome of this labor-side negotiation, labor activists, including the AFL-CIO have used the side agreement’s citizen petition process to highlight ongoing political campaigns and struggles in their home countries.[sup]
[32][/sup] He claims that despite the relative weakness of the legal provisions themselves, the side-agreement has served a legitimizing functioning, giving certain social struggles a new kind of standing.
Unions have recently been engaged in a developing field of transnational labor regulation embodied in corporate codes of conduct. However, O’Brien notes that unions have been only peripherally involved in this process, and remain ambivalent about its potential effects.[sup]
[33][/sup] They worry that these codes could have legitimizing effects on companies that don’t actually live up to good practices, and that companies could use codes to excuse or distract attention from the repression of unions. Braun and Gearhart note that although unions do participate in the structure of a number of these agreements, their original interest in codes of conduct differed from the interests of human rights and other non-governmental activists. They believed that codes of conduct would be important first steps in creating written principles that a company would be compelled to comply with in later organizing contracts, but did not foresee the establishment of monitoring systems such as the Fair Labor Association. These authors point out that are motivated by power, want to gain insider status politically and are accountable to a constituency that requires them to provide them with direct benefits. In contrast, activists from the non-governmental sector are motivated by ideals, are free of accountability and gain legitimacy from being political outsiders. Therefore, the interests of unions are not likely to align well with the interests of those who draft and monitor corporate codes of conduct.
Arguing against the idea that high union wages necessarily make manufacturing uncompetitive in a globalized economy is labor lawyer
Thomas Geoghegan. Busting
unions, in the U.S. manner, as the prime way of competing with China and other countries [does not work]. It's no accident that the social democracies, Sweden, France, and Germany, which kept on paying high wages, now have more industry than the U.S. or the UK. … [T]hat's what the U.S. and the UK did: they smashed the unions, in the belief that they had to compete on cost. The result? They quickly ended up wrecking their industrial base.[sup]
[34][/sup]
Unions have made some attempts to organize across borders. Eder notes that transnational organizing is not a new phenomenon but has been facilitated by technological change.[sup]
[35][/sup] Nevertheless, he claims that while unions pay lip service to global solidarity, they still act largely in their national self-interest. He argues that unions in the global North are becoming increasingly depoliticized while those in the South grow politically, and that global differentiation of production processes leads to divergent strategies and interests in different regions of the world. These structural differences tend to hinder effective global solidarity. However, in light of the weakness of international labor, Herod notes that globalization of production need not be met by a globalization of union strategies in order to be contained.[sup]
[36][/sup] He points out that local strategies, such as the United Auto Workers’ strike against General Motors in 1998, can sometimes effectively interrupt global production processes in ways that they could not before the advent of widespread market integration. Thus, workers need not be connected organizationally to others around the world to effectively influence the behavior of a transnational corporation.