What broke the long stalemate on a multi-year aviation bill was a Jan. 20 deal between Senate Majority Leader Harry Reid (D-Nev.) and House Speaker John Boehner (R-Ohio) concerning a 2010 National Mediation Board rule that changed requirements for airline and railroad workers' unionization elections.

The NMB regulation was seen a plus for organized labor. The 2011 House-passed bill would have abolished the rule but last year's Senate-approved version would have left it in place.

Reid and Boehner agreed to modify the NMB rule and their deal cleared the way for the House and Senate conferees to settle several other remaining issues. The Washington Post has reported that some unions are unhappy with the Reid-Boehner compromise.

Updated Feb. 1 with news of conference report filing, background on labor provision deal, and added links.