A federal judge slapped the American Airlines mechanics unions with new, heavier restrictions that could include fines and other discipline for maintenance workers who turn down overtime and off-site assignments.

In the ongoing battle between American Airlines and its mechanics, U.S. District Judge John McBryde approved the company's request Wednesday night for an order forcing the two unions overseeing maintenance workers to take more drastic steps to end an alleged work slowdown.

American Airlines has argued a June 14 court order didn't stop a coordinated effort to slow down work, resulting in flight delays and cancellations for thousands of passengers.

The new order doesn't say what kind of discipline and fines mechanics could face, but the unions are under pressure to comply with the judge's orders or face steeper consequences down the line. Union representatives declined to comment.

An American Airlines mechanics' union flier submitted in court filings promises the "bloodiest, ugliest battle" in labor history.

American Airlines has accused the union of a coordinated effort to turn down overtime work, off-site assignments and not having planes ready when they need to take off the next morning -- all to pressure the company during contract negotiations reaching back four years.

The two sides met in a trial on July 1, and McBryde should decide later this month whether to make his temporary order permanent.

The International Association of Machinists and Transport Workers Union representing about 31,000 American Airlines mechanics and other workers testified in court that they did everything they could to tell workers to stop efforts to punish American Airlines.

The new, stronger order could be a hint that McBryde favors American in the case, said Michael Green, a labor law professor at Texas A&M University's School of Law in Fort Worth.

"It doesn't mean that it foretells the ultimate decision, although part of it suggests that," Green said.

It's tricky to point out exactly which employees may be behind the alleged slowdown because no one is required to take overtime or off-site work assignments. American Airlines managers said they haven't brought complaints about any individuals they suspect of slowing down work, but pointed to statistics that show an across-the-board problem.

On Wednesday, American Airlines filed testimony from managers in Philadelphia and Dallas who said all requests for overtime were being turned down for stretches of a week or more. They said they were told the overtime prohibition would then move to another site.

The new restrictions also call for union leaders to post more notices, conduct meetings and make videos telling workers to stop any coordinated efforts to slow down work.

A restraining order like this is an unusually strong step in a labor negotiation case, Green said, although it might be necessary if American Airlines is in fact hurt by worker slowdowns. Essentially, American is putting the onus on the unions to police its own members.

"The intent here is not to go after individual employees here or there, it's to go after the union," Green said.