London Underground (LU) drivers have voted to strike on Boxing Day in a row over pay.
The union Aslef said LU was insisting 26 December was a normal working day but the union wants its members to receive additional pay.
It said staff should be compensated for working at "highly unsocial times".
But Transport for London (TfL) said a long-standing agreement covering staff working arrangements on Boxing Day was in place with all trade unions.
Aslef wants triple pay and a day off in lieu for drivers working on 26 December.
According to the union its members voted 9-1 in favour of industrial action which threatens to disrupt travel for football fans and Christmas shoppers.
Aslef general secretary Keith Norman said: "It is painfully obvious to any reasonable person that Boxing Day is not an ordinary working day and therefore it is no surprise that Aslef members have reacted in the way they have."
A TfL spokesman said: "It is disgraceful that Aslef should try to hold Londoners and London Underground to ransom in this way.
"LU has made every effort to resolve this issue with the Aslef leadership, which has refused to attend talks at Acas to discuss its claim for triple time and a day in lieu for its members."
Tube services have been disrupted in recent weeks by a series of strikes in a separate row over jobs.