ATLANTA — 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 pilots before the carriers' merger announcement, discord is growing between Northwest pilots and their national union, which also represents Delta pilots.

The Delta-Northwest Airlines 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, said Minneapolis airline consultant Terry Trippler. "What they're trying to say is, 'Don't sign that contract; let's try to renegotiate one that includes all of us."'

In spite of their objections, Prater signed the contract May 30, according to the Northwest pilots union in a message to members.

Now, "you have a situation where different locals of the same union are vying with each other," said Gary Chaison, professor of labor relations at Clark University in Worcester, Mass. "You have Northwest pilots believing they're at a disadvantageous position relative to the other agreement."

ALPA International said in a written statement that "we have every reason to believe (a joint agreement) can be accomplished."

Delta's pilots union said Prater had already signed a transaction framework agreement that obligated him to sign the contract.

Kelly Regus, a spokeswoman for the Delta pilots group, said the contract "set the bar" for a joint agreement, which is expected to address pay and work rules. That would be followed by negotiations on seniority lists, one of the stickiest issues in a merger. Pilot seniority can affect furloughs and can influence everything from pay to work schedules.

Northwest pilots want the same pay as Delta pilots as soon as the deal closes, but Delta management plans to propose a phase-in of pay increases, according to the Northwest pilots. Delta executives have met with Northwest pilot union leaders, and meetings with negotiators are scheduled for this month.

To some, it appears the friction between the two pilot groups could lead to the type of conflict that has affected the US Airways-America West merger for more than two years, because pilots were unable to agree on how to integrate seniority lists.

The two pilot groups still work under separate contracts and are now represented by different unions.

In the proposed Delta-Northwest merger, "there could easily be legal challenges and a lot of problems. And there could be a feeling that they need separate union representation," Chaison said. "America West and US Air indicate how messy (mergers) can be in terms of labor relations."

Delta officials have said they still hope to reach a joint contract with the pilots before the merger is approved.