The International Assn. of Machinists and Aerospace Workers -- which represents about 14,000 US Airways machinists, mechanics and fleet service workers -- has been trying to negotiate a new contract with US Airways for more than two years. It complains that its workers earn about 10% less than their counterparts at American Airlines.

The federal National Mediation Board has been called in to try to broker an agreement between the airline and the union, but union officials say no progress has been made.

The US Airways union asked the mediation board Wednesday for a release from negotiation, which would trigger a 30-day cooling-off period. If no deal is reached after the 30-day period, the union would be free to strike.
Newly merged American Airlines faces labor problems - latimes.com