Unite is to launch a legal challenge against British Airways' plans to impose new pay and conditions on 14,000 cabin crew, the union said today.
The union said it will apply for a High Court injunction "against the imposition of new contracts" for the cabin crew, which it says are due to be brought in on November 16.
The action is separate to a ballot for industrial action which is also planned, a spokeswoman said.
The move comes as BA faces possible Christmas strikes following a lengthy and unresolved dispute over its cost-cutting proposals.
BA has announced plans to cut staff numbers by 3,700, in addition to a reduction of around 2,500 achieved between June 2008 and March 2009.
Earlier this week, BA said it was "extremely disappointed" at the move to ballot workers, insisting it was not planning to change terms and conditions of current crew.
But Unite said it had "no alternative" but to ballot its members in a bid to persuade BA not to impose "unacceptable contractual changes".
Cabin crew had already decided to hold an emergency meeting on Monday to decide whether to fight plans to cut jobs, freeze pay and introduce worse wages and conditions for new staff.
Thousands of workers are expected to attend the meeting, at Sandown Racecourse in Surrey, two weeks before the cuts come into effect.
Two former sections of the Transport and General Workers Union - Bassa and Cabin Crew 89 - have joined forces for the first time in more than 20 years to hold the joint meeting.
A BA spokesman said: "We understand that Unite's lawyers have been to the High Court this morning and issued proceedings for an injunction application.
"The union has not yet served us with the papers.
"We have announced changes to onboard cabin crew numbers to enable us to accept more than 1,000 requests from crew for voluntary redundancy and more than 3,000 requests for part-time working.
"Our announcement followed more than nine months of negotiation and consultation with Unite.
"The changes do not alter contractual terms and conditions for individual crew members. British Airways is facing very difficult economic conditions and is heading for a second consecutive year of financial losses for the first time in our history.
"Everyone within the company knows we must reduce our costs to move back toward profitability."Reuse content