That's a helluva question Bob! For the great unwashed masses out here in non-union land would you mind gving a brief education on class & craft? Also perhaps how other airlines, NMB define these issues?
This stuff just confuses me to a certain extent, so any insight you could provide would be helpful.
Unfortunately when it comes to the NMB things get more confusing the more you dig but basically what it comes down to is this;
The RLA was put in place in 1926 because numerous strikes in the Railroad industry were hurting commerce.
You see while the Railroads were pretty effective at busting unions they just kept popping up. So they may bust the union in NY only to have one in OHIO go on strike and after they busted them a new group would pop up in Chicago and before they got done with them another one would pop up in NY. Any group along the line could shut it down, even if it was temporary. This created an intolerable situation for the fat cats.
In order to prevent this the RLA was formed and with it the National Mediation Board, NMB. Their job is to make workers believe they have certain rights and protections and, most importantly, to keep things moving. So the NMB made a pact that was favorable to companies and big unions but weakened the workers. Workers were now very restricted from using their labor to make gains. In exchange for pretty much giving up the right to strike unions were given a closed shop, guaranteed dues flow.
Class and craft has to do with how workers become unionized. Instead of workers being organized by location they were divided up into class and craft depending on what type of work they did. In order for any class of workers to get a union the entire class and craft had to be organized. Only larger unions had the resources to travel cross country and organize.
So if mechanics in New York want a union they have to convince mechanics across the country, and anyone else who the NMB determines is in their class and craft, that they should join the union too, even though conditions could vary greatly depending on geographic location. If there is no union in place they only need to get a little more than a third of the "class and craft" to initiate a representational election. If there is a union in place they need to get 50%+1. If they dont get at least half plus one of those elibible to vote across the entire country to vote, they dont get a union.(Imagine if we had the same standards for politicians?!)
Here is another catch, the NMB will not tell mechanics which workers are part of their class and craft until after they file, thats why it varies from time to time. Pilots and Flight attendants are pretty much the only clearly defined groups. This little gotcha is what also helps buy the loyalty and cooperation of the unions to the NMB,it makes it very hard for workers to replace unions that are in bed with the company. Once a union files for an election and its determined that they did not have enough cards to call for an election they can not file again for another year. A year gives the union and the company plenty of time to weed out anyone that threatens their little deal.
The NMB, remember their primary duty is to keep things moving, will often tweek things in order to thwart raids. They mediate between unions and companies so if both parties come to them and say how well they have worked things out-ie-no interuptions to commerce- and this new organization is trouble-ie-disruptions, strikes etc, the NMB will alter the class and craft as much as they can in order to maintain the status quo. In some cases the NMB has allowed companies to add the names of dead people, retired people and people who never even worked for the company to be included on the eligibility list in order to prevent an election. Its hard enough to get a majority of people to vote, let alone dead ones.
Hope I didnt stray off too far and I hope it helps.