London Underground today launched legal action in a bid to halt a planned strike on Boxing Day by Tube drivers in a row over pay.
The company said it was challenging the validity of the strike called by the Aslef union's leadership over its claims for additional Boxing Day pay.
The union announced last week it was calling four 24-hour strikes in the coming weeks, claiming LU was offering no extra pay for working the bank holiday.
LU said Aslef was seeking triple pay and an extra day off for working on Boxing Day, adding that the drivers already earned a premium in their annual salary for working on public holidays.
Howard Collins, LU's chief operating officer, said: "This threat of strike action is disgraceful, and Londoners will share our disbelief at these outrageous claims by Aslef's leadership for even more money to work on a day for which their members are already being paid.
"LU has a long-standing agreement with all of its trade unions which covers working arrangements on public holidays, and Boxing Day is included in that.
"The underground is a public service that should be playing its part in helping Londoners and the capital have a happy and prosperous Christmas, and we will take every possible step to ensure that happens."