London Underground drivers are to stage three strikes, including one on Boxing Day, in a row over Bank Holiday pay.
Members of Aslef will walk out for 24 hours on December 26, and again on January 18 and 25, threatening travel chaos in the capital.
The move was announced after Aslef members voted by 9-1 in favour of strikes in a long-running row over extra pay for working on Bank Holidays.
An Aslef spokesman said: "The ballot result shows the strength of feeling that remains on this issue. The union is committed to finding a solution which offers voluntary working and compensates those who do attend."
It will be the third successive Boxing Day walkout by Tube drivers in a dispute over Bank Holiday pay which dates back to an agreement in 1992.
The stoppage will disrupt Tube services on a busy day in the capital, causing chaos for shoppers, sports fans and visitors. Talks have been held at the conciliation service Acas, but the dispute remains deadlocked.
Howard Collins, London Underground's chief operating officer, said before the strike dates were announced: "We have been in discussions with the Aslef leadership to find a way to end this dispute and we made what we believed was a very fair offer.
"Unfortunately, this was not accepted and the offer has now been withdrawn so that further options to resolve the issue can be explored with the union at Acas.
"LU has a long-standing agreement with all trade unions which covers working arrangements on Bank Holidays, including Boxing Day. However, we have shown good faith and tried to find ways forward.
"Further industrial action will not achieve anything and I would urge Aslef leadership to work with us to resolve this dispute."