United Airlines said on Wednesday it asked a federal judge to stop four of its pilots and their union from what it called illegal job actions that have caused hundreds of cancelations.

United said some pilots have been abusing sick time because they oppose its plan to shrink its fleet and furlough pilots. United said the request for an injunction also aims to end intimidation of pilots who pick up extra flying time, saying that amounts to an unlawful work slowdown.

"It is absolutely irresponsible for ALPA to promote unlawful behavior," especially when the industry is fighting high fuel prices, said United Chief Administrative Officer Pete McDonald in a statement.

An ALPA spokesman did not immediately return a phone message seeking comment.

The airline tried to negotiate a solution with the union and had increased the number of pilots on reserve, but talks with the airline broke off late last week, United Chief Operating Officer John Tague said in a message to employees.

"Despite these significant steps, unlawful job actions escalated, intimidation of pilots continued and the impact on our customers and other employees grew to truly unacceptable levels," he said.

Shares of Chicago-based UAL Corp., United's parent, fell 72 cents, or 8.5 percent, to $7.79 in afternoon trading. Airline shares were generally down on Wednesday after oil prices rose.