United Airlines, a subsidiary of UAL Corporation with corporate offices in Chicago, the United States, has won a preliminary court injunction against a pilots’ trade union preventing it from taking industrial action against the airline.

US District Court Judge Joan H Lefkow ruled that that a sickout and work slowdowns by some pilots of United Airlines pilots in the summer of 2008 was illegal.

The judge said pilots of United Airlines “went too far with some illegal sickouts” earlier in 2008.

United Airlines said in a statement that the sickouts alone caused the cancellation of 329 flights between July 19, 2008, and July 27, 2008, and that that the company lost about $8 million (£5.3 million) in revenue and $3.9 million in operating profits.

The airline also argued that some pilots were carrying more fuel than needed and were taking the so-called “work-to-rule” actions, such as refusing to take off in planes with minor mechanical issues that did not require immediate attention under federal rules.

United Airlines had filed the lawsuit against the pilots union and four individual members on July 30, 2008.

However, the Air Line Pilots Association (ALPA) denied having encouraged the United Airlines pilots’ action, which has been barred under airlines’ labour laws.

Sickouts or slowdowns are barred by the Railway Labor Act, the labour law governing labour relations in the airline industry.

The United Airlines branch of the ALPA issued a statement saying it had “already advised the United Airlines pilots that it remains essential not to engage in any form of economic action involving United Airlines.”

However, US District Court Judge Joan H Lefkow made it clear in her ruling that she did not believe what the union said.

The United Airlines branch of the Air Line Pilots Association union has been in dispute with the airline over what it describes as the company’s refusal to reverse concessions that the union gave in 2003 during United Airlines’ bankruptcy reorganisation, including 40% pay cuts.

A statement from United Airlines said that, in the summer of 2008, “pilots calling in saying they were fatigued more than doubled, from one call a day to more than two-and-half a day.”

United Air Lines, the third largest carrier in the United States, has its largest hub at O’Hare International Airport, Chicago, the United States. It also has hubs at Denver International Airport, Washington Dulles International Airport, San Francisco International Airport, and Los Angeles International Airport as well as maintains focus-city operations at Narita International Airport near Tokyo in Japan.