Northwest Airlines Corp. flight attendants rejected a wage-cutting contract yesterday and warned of random, unannounced strikes as early as mid-August.

Northwest said a strike — which could spook travelers and hinder the airline’s bankruptcy restructuring — would be illegal and that it would seek a court order to block one. The union pledged to give 15 days’ notice before any strike, a move it had not made as of yesterday night.

Northwest has sought $1.4 billion in annual labor savings as it reorganizes in bankruptcy court. Flight attendants are the last union at Northwest, the nation’s fifth-largest carrier by the standard industry measure, without a wagecutting contract. But the airline’s deals with pilots and ground workers don’t take effect until there’s a new contract for flight attendants, too.

Northwest moved quickly to impose a new contract after 55% of flight attendants voted down the tentative agreement on Monday. Flight attendants had rejected a slightly different tentative agreement in June.

“This decision is an example of the flight attendants’ determination not to watch their livelihoods be squandered by management,” a spokeswoman for the Association of Flight Attendants, Corey Caldwell, said.

Before yesterday, Northwest already had permission from a bankruptcy judge to impose the terms of an earlier tentative agreement that 80% of flight attendants rejected in June. Northwest has been seeking worker pay cuts since 2003, and yesterday it said time was up.

“Notwithstanding the results of the flight attendants’ contract vote, Northwest must continue to move forward with its restructuring efforts,” the senior vice president of human resources and labor relations, Mike Becker, said in a statement.

Its new agreements with pilots and ground workers cannot take effect until it has a new contract with flight attendants, too — either one that workers approve, or one the company imposes on them.