The Unite union is taking British Airways back to the high court in a bid to overturn changes made to cabin crews’ working arrangements, as the carrier prepares to report a large quarterly loss.

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 onboard crewing levels from 15 to 14 on long-haul flights from London’s Heathrow airport.

But Unite, which last year failed its attempt to get a high court injunction to block the airline’s plans, said it was not consulted properly on the changes.

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 cost cuts are essential to safeguard the long-term future of the airline.

“Revenues are well down and it is essential we reduce costs to ensure our long-term survival. Thousands of staff across the airline have already made contributions to the cost-reduction programme,” BA said in a statement.

BA reported a first-half loss of £292m and is expected to report an average pretax loss of £627.76m for the year to the end of March, according to a poll of analysts.

The British carrier posts third-quarter results on Friday and is expected to report another considerable loss.

Unite is in the process of re-balloting its members after BA last month won a court ruling to prevent a cabin crew strike that threatened to strand around a million passengers over Christmas.

The new ballot closes on February 22.

The court hearing, expected to last five days, will resolve whether there should be a permanent injunction preventing BA from imposing cost-cutting proposals.