American Airlines says a work slowdown by its mechanics could affect 3,400 passengers a day if it continues into summer.

The airline says its mechanics and their unions are conducting the illegal work slowdown to gain leverage in contract talks.

In a lawsuit filed Monday, American said that from Feb. 4 through May 13 more than 640 flights were canceled and 270 flights were delayed by at least two hours because of unavailable planes, the Associated Press reports. The cancellations and delays upset travel plans for 125,000 people.

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American filed the suit in federal district court in Fort Worth, Texas, against the Transport Workers Union of American, AFL-CIO, International Association of Machinists and Aerospace Workers and Airline Mechanic and Related Employee Association, CBS News reports.

The airline is asking a judge for a preliminary injunction to force the slowdowns to stop.

If the work slowdowns persist at current levels during the peak summer travel season, American said, an additional 2,200 flights could be canceled or delayed for two hours or more, USA Today reports. That would affect more than 300,000 passengers.

"Allegations of a slowdown are unfounded," John Samuelsen, president of the Transport Workers, said. "This is an intimidation tactic by AA because the union is fighting back against their efforts to offshore thousands of solid blue collar Jet Mechanic jobs into South America. We will continue to battle AA to keep these jobs on USA soil and in doing so, ensure the safety of air travelers."

Samuelsen said moving more work outside the U.S. could threaten the jobs of 6,000 mechanics, AP reported.

An airline industry trade group is predicting record-high summer travel with about 2.8 million travelers a day.

Airlines for America expects 257.4 million people will fly on U.S. carriers between June 1 and Aug. 31, AP reported. That's a 3.4% increase over last summer.

The American Airlines dispute is similar to one earlier this year between Southwest Airlines and its mechanics union. Southwest sued in March, but the two sides agreed to a tentative contract.