The two sides have been negotiating a new contract since 2005.
America West airlines bought US Airways that year, but pilots from the two airlines still fly different planes under separate union contracts.
The US Airways Pilots Association says the talks are “hopelessly stalled.”
A US Airways spokesman says it has not seen the request for a mediator and has no comment.
Federal mediation is a common step in airline negotiations, which often drag on for years.
The union is in a legal fight with former America West pilots over seniority. Oral arguments are planned next month in the federal Ninth Circuit Court of Appeals.