It's just what Delta Air Lines executives were trying to avoid. In the wake of failed attempts to reach a joint agreement with Delta and Northwest Airlines pilots before the carriers' merger announcement, discord is growing between Northwest pilots and their national union, which also represents Delta pilots.

The Delta-Northwest merger was announced in April with a proposed deal for Delta's roughly 7,000 pilots but no deal with Northwest's 5,000. The two pilot groups had reached an impasse over how to integrate their seniority lists.

If the merger is granted regulatory approval, it is expected to close by the end of the year.

But Northwest pilots have come into conflict with the head of the Air Line Pilots Association International because the proposed deal includes annual pay raises and an equity stake for Delta pilots. Both unions are separate units of ALPA.

The Northwest pilots' union leadership said it asked ALPA International President John Prater not to sign the Delta pilots' labor agreement.

"Northwest pilots were kind of left standing on the side" after Delta pilots ratified the agreement, Minneapolis airline consultant Terry Trippler said. "What they're trying to say is, 'Don't sign that contract, let's try to renegotiate one that includes all of us.' "