A US federal judge has ordered the pilots union at United Airlines to end an "unlawful campaign of sick leave abuse, pilot intimidation and other actions" that has caused hundreds of flight cancellations.

The airline's parent, UAL, said on Tuesday the court granted a motion for preliminary injunction against the Air Line Pilots Association (ALPA) and four individual pilots that UAL has accused of deliberately disrupting operations.

UAL alleges the union actions were payback for the company's decision to cut 950 pilot jobs this year.

"This is an important ruling because it means our customers and employees will not be subject to ALPA's illegal actions intended to disrupt our operations and intimidate our employees," said Pete McDonald, UAL's chief administrative officer.

ALPA said in a statement it would comply with a court order.

"ALPA has already advised the United pilots that it remains essential not to engage in any form of economic action involving United Airlines," the union said in a statement.

The company, which plans to have the injunction made permanent, has said it was forced to cancel 329 flights between July 19 and 27, costing it millions of dollars in potential profit and disrupting travel plans for some 36,000 people.

UAL said the union had engaged in a campaign to encourage members to adhere strictly to contract terms and refuse voluntary assignments as a way of pressuring management to open contract talks early. The current contract expires at the end of 2009.

UAL also said the union and four pilots organized abuses of the company's sick leave policy in response to plans announced in June to eliminate 950 pilot jobs as part of capacity cuts.

The airline industry is rapidly shrinking as part of a plan announced in the first half of 2008 to combat fuel prices.

UAL has said it would cut domestic capacity by 14 percent in the fourth quarter. The downsizing also would eliminate about 7,000 jobs, or 13 percent of the work force United had when cuts were announced earlier this year.

The cost of fuel peaked in July and has since dropped. Carriers are going through with the downsizing, however, and has retained fare pricing power that helps the industry survive as economic weakness erodes travel demand.