Date of hire. Pure and simple.
PITbull has a great point. Here's the situation for flight attendants at US Airways, very loosely: They have a seniority list that is twice the size of the airline as it currently exists, which means only half of the system seniority list is active at mainline. There are about 10,000 on the seniority list, 5000 or so are active at mainline. Most senior is 1950-something hire, most junior active is 1999. Out of the furloughees, about 2000 are involuntarily so.
Roughly a third to half of the active F/As want to leave. The company got more responses for the early buyout than what they were offering.
Then there is the MidAtlantic division, which is basically a division where you do mainline-type flying but for under a crap contract. It is staffed by involuntarily furloughed mainline F/As in seniority order. They can stay furloughed if they like, whether they do MAA or not doesn't affect thier recall status. There are only 350 at the moment, but they are still filling positions with willing furloughees every time they become available. Most senior MAA is 1999, most junior is 2001 when US stopped hiring and started mass furloughing. There are still people awaiting an offer even for MAA.
So you have a company that has senior employees wanting to leave, and junior employees wanting to come back, clearly regardless of the conditions. A truly unlimited recall would benefit everyone- the company regains a more junior and willing workforce, and the people who are done get to leave with a bit of incentive and dignity.
As for America West, considering they have hired so much in the last five years alot of junior people would be affected by a merger, and that sucks when there are many people who don't even want to be with the company anymore but don't have incentive to leave. Let's have a new airline with people who want to be there. It would be better for all to have new hires coming in below all of us in a cycle of growth. And if you were running a customer service intensive business, which employee attitude do you think would be better for your product and operation, and therefore your bottom line?
Also, and I know I harp on this all the time, but if they do let contract "regionals" fly the 170/190 family, there will be no space for anyone at the shrinky-dink that will be left of a "mainline" anyway. There will clearly be growth with that aircraft, both as replacement for 737 and RJ flying, and just plain growth. Let's keep as much flying ours as possible to avoid kicking people onto the street.
If US-HP is going to be this revolutionary major network LCC, then the unions should be revolutionary and demand simplicity like the LCCs. JetBlue will fly the 190s, and it will be JetBlue, not some company posing as JetBlue Express. There should be a single list for all flying at the new entity. This airline and it's future should be an opportunity for US Airways and America West employees to operate a great airline, not a host for a bunch of parasite companies to feed off of and be pawn's for an evil empire.
I even think the RJs and Dash 8s should be on the same list, and the W/O'd employees merged in in seniority too. One company, much more job security for everyone, and alot more teamwork and good morale. Simplicity- no infighting, no company trying to push scope issues or outsource. I say if they want a big LCC airline, then they make it an airline (singular), not a franchise.
And I'd like to see the two groups negotiate a new contract together, covering all of the flying, that is competitive and smart. As well as beneficial to it's members both financially and quality of life wise.
*Off my soap box*