Rival unions are fighting over how to represent 24,000 flight attendants at the new American Airlines, which expects to merge with US Airways next month.
Cabin crews at Fort Worth-based American are represented by the Association of Professional Flight Attendants.
Their US Airways counterparts belong to the Association of Flight Attendants.
APFA President Laura Glading on Wednesday she said refused to begin new talks on a proposal drafted by the US Airways side.
The dispute involves a "concessionary" labor contract negotiated last spring between the APFA and US Airways management. It was part of US Airways CEO Doug Parker's strategy of winning support for a merger from American's unions while he negotiated with American Airlines management.