WASHINGTON -- United Airlines' mechanics filed suit Monday to block an emergency panel established by President Bush that delayed the union from striking last month, according to a wire service.

The International Association of Machinists and Aerospace Workers union wants a federal judge to set aside Bush's executive order establishing the board. Creation of the board prohibits a strike for at least 60 days while the panel works to reach an agreement between the union and airline, based in the Chicago area. Overturning Bush's order would clear the way for the union to strike.

Bush acted after the National Mediation Board, which oversees labor relations in the airline and railroad industries, recommended he intervene and create a board to help break the two-year stalemate. The union, which represents 15,000 United mechanics, had been set to strike the weekend before Christmas.

National Mediation Board spokesman Dan Rainey said federal mediators had no comment. United Airlines spokesman Chris Brathwaite said the Elk Grove Village, Ill.-based carrier is “completely confident that there will not be an interruption of service” as a result of the mechanics' lawsuit.

“Customers should continue to book on United with confidence,” Brathwaite said. “We believe in the process already established by the National Labor Relations Board and we remain committed to working with the IAM and the U.S. government toward a resolution.”

The lawsuit claims the board did not meet a legal threshold when it recommended the panel to Bush. The union claims the overriding reason was to avoid a strike during the holiday.

The union and United “could have concluded their negotiations but for the White House's interference,” said union President Tom Buffenbarger. “In this instance the NMB behaved more like a puppet on a string than a neutral federal agency.”

Federal mediators have recommended three airline emergency boards since Bush took office last year. In the previous 35 years, an emergency board was established only once.

The emergency board will hold its first hearing Wednesday in Washington.

In late trading on the New York Stock Exchange, shares of United parent UAL (NYSE:UAL - news) were down 4 percent, or 59 cents, at $15.05 a share.