London Underground train drivers have voted to strike on December 26 in a dispute over extra payments for working on the Boxing Day public holiday, the Aslef union said on Wednesday.
Around 60 percent of the underground system's drivers are Aslef members and the action would affect all the network's lines, a spokesman said.
If the strike goes ahead, it could hit struggling retailers hoping to attract large crowds of shoppers to traditional post-Christmas sales in central London.
Operator London Underground said the claim for extra pay was outrageous and went against a long-standing union agreement that staff would work as normal on some public holidays.
It said it had already reviewed the level of service needed on the December 26 holiday so that only a quarter of drivers would need to work.
Aslef said it had won a 92.3 percent vote in favour of action after balloting the 2,200 drivers in the union. A turnout figure was not immediately available, but the spokesman said it was exceptionally high.
London Underground was seeking volunteers to work on December 26 but was not offering any offering additional payments, the union said. Its members may require substantial incentives to volunteer, it added.
Further action would take place on January 16, February 3 and February 13 if the dispute was not resolved, the union said.
London Underground said it was disgraceful that Aslef was threatening a strike while talks on the issue continued.
The threat of strike action will not achieve anything and I urge Aslef to join us in our commitment to resolve this matter through discussions, said London Underground Chief Operating Officer Howard Collins.
(Reporting by Tim Castle; Editing by Steve Addison)