The Unite union took BA to the High Court in a bid to overturn changes to cabin crews' working arrangements.
BA wants three quarters of its crew to accept a pay freeze this year, and for 3,000 staff to switch to part-time working, along with a reduction in on-board crewing levels from 15 to 14 on long-haul flights from London's Heathrow airport.
Unite, which last year failed in a previous attempt to get a High Court injunction to block the airline's plans, said it was not consulted properly on the changes.
The union is re-balloting its members after BA won a court ruling to prevent a cabin crew strike that threatened to strand about a million passengers over Christmas. The new ballot closes on Monday.
"We are extremely pleased with today's High Court ruling that the modest changes we made to onboard crew numbers on flights from Heathrow were reasonable, did not breach crew contracts and can remain in place," BA said in a statement.
Reversing the changes would have a severe financial impact on the company "when we are facing a second year of record annual losses," it said.
BA argues that it is entitled to cut the number of cabin crew on board its Worldwide and Eurofleet flights as these are not terms of individual cabin crew members' contracts and that the cuts -- designed to save 140 million pounds ($215 million) a year -- are vital to safeguard the airline's long-term future.
Len McCluskey, Unite assistant general secretary, said: "Today's regrettable judgement makes absolutely no difference to the substance of our dispute with British Airways.
"We remain in negotiations with the company and hope that management will address the real concerns of cabin crew. Should they fail to do so industrial action remains a possibility," he said in a statement.
BA urged Unite to "reflect on the court's decision rather than impose an unnecessary strike on the travelling public."
BA this month posted a surprise third-quarter operating profit of 25 million pounds, helped by heavy cost cutting, but said it was still in a worse position than last year, despite attempts to adapt to the realities of global recession.
Pilots at Germany's flagship airline Lufthansa are to hold a four-day strike starting on Monday in a dispute over pay and job security. (Reuters)
