The International Association of Machinists and Aerospace Workers (IAM) recently completed negotiations with United Airlines covering 28,000 employees, but is still working through issues in negotiations with US Airways which would cover 3,500 employees. The talks may have floundered when mediation was requested, but unavailable due to the Federal government shutdown. The IAM recently defeated the teamsters union in a certification election after United and Continental merged, and is the only US Airways union that supports a merger with American Airlines. The IAM is using the deal, which included immediate wage increases ranging from 7% to 29%, with United as an anchor for how negotiations with US should go.
See "Machinists Union Ratifies United Contract But Says US Airways Drags Its Feet", Ted Reed, Forbes.com, October 29, 2013