London Underground is taking legal action in a bid to prevent a Boxing Day strike by Tube drivers going ahead.
Members of the drivers' union Aslef are due to stage a 24-hour walkout on Sunday over a claim for triple pay and a day off in lieu.
Transport for London said it had asked the union to withdraw their action otherwise LU will go to court.
A spokesman said : "LU is currently seeking an injunction to prevent the potentially disruptive and completely unnecessary strike action called by the leadership of the Aslef union. The union has unilaterally ripped up a long-standing agreement on pay and working hours that gave LU employees increased pay and 6.8 weeks holiday in return for working some bank holidays, including Boxing Day.
"We have tried to resolve this dispute through negotiation, but our offer to reduce the number of drivers rostered to work on Boxing Day was flatly rejected and union representatives walked out of talks at Acas. This left us no option but to seek a legal solution".