HONOLULU -- The Aloha Airlines pilots' union threatened Friday to strike as soon as April 26, saying the airline has violated the union's collective bargaining agreement.

The bankrupt airline shut down passenger service earlier this month, but has retained about 40 of its 312 pilots to operate its profitable interisland cargo operation. An auction of Aloha Airlines cargo is set for Monday.

The Air Line Pilots Association has complained Aloha violated its labor agreement by keeping less senior pilots on the payroll to fly cargo routes. The airline began training more senior pilots to fly cargo planes this week, saying that less senior pilots of its 737-200 cargo planes would be terminated.

In a filing Friday in federal bankruptcy court, ALPA said although the bankruptcy code provides for rejection of collective bargaining agreements after strict requirements are approved by a bankruptcy judge, Aloha has never asked for or received relief from the court.

Aloha now wants to sell the cargo operation. The union said its agreement requires a new buyer to keep the same pilots.

"Aloha will make as a condition of any sale transaction that the purchaser will employ Aloha pilots in seniority order. Aloha management has been unwilling to do that," said James Linsey of ALPA.

"It is regretful that the Air Line Pilots Association (ALPA) is again trying to hype the media with the threat of a strike as a negotiations ploy. No such legal right exists under the law and Aloha will take necessary legal actions to prevent any disruption to the flow of air cargo in Hawaii," Aloha spokesman Stu Glauberman said.

The union claims Aloha improperly terminated its pilots, instead of furloughing them, to avoid paying them furlough pay as called for in their union agreement. ALPA also said Aloha violated seniority rules, keeping pilots hired within the last six months while terminating much more senior pilots, including one who had been with Aloha for 29 years.