Rail union leaders have threatened to introduce an overtime ban on London Underground over the Christmas period.
The 500 engineering and electrical workers could take the action following a dispute over pay and the rejection by Unite union members of a two-year pay deal.
The deal, made by London Underground, was a 1.5% pay rise this year followed by an inflation-plus 0.5% rise in 2010-11.
Unite members voted against a full strike, opting instead for an overtime ban.
John Morgan-Evans, regional officer for Unite, said there was a “strong possibility” that the ban would occur.
He added: “It would have an effect on services because our members are responsible for getting Tube trains ready for service, as well as maintenance and safety.”
London Underground has called on Unite to continue discussions with the company, the BBC has reported.
The train operator said only one-quarter of its members voted for industrial action because less than half took part in the ballot.
Richard Parry, managing director of London Underground, said: “The Unite leadership has failed in its bid to get a mandate for strike action and I urge them to return to meaningful discussion now.
“There is absolutely nothing to be gained from taking more strike action in the current tough economic climate at a time when many Londoners have seen their pay frozen or have lost their jobs this year.”
The ban, and a work-to-rule policy, will begin on 7 December.