I don't know if this is the answer but it makes for interesting reading:

http://www.expressjetpilots.com/the-...ny-mohawk.html

On May 16, the Senate Commerce Committee added an amendment to the FAA Reauthorization bill (the Aviation Investment and Modernization Act of 2007, S.1300) that would impose Allegheny-Mohawk Labor Protective Provisions (LPPs) on any future airline mergers or acquisitions. If the bill is approved with this amendment, it will significantly impact the financial feasibility of future airline mergers and acquisitions. It could also nullify existing merger provisions in collective bargaining agreements negotiated between airlines and unions.
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A requirement that provisions be made for the integration of seniority lists "in a fair and equitable manner," including, where applicable, agreement through collective bargaining between the airlines and the representatives of the employees affected.