London Underground drivers are to stage a series of 24-hour strikes in the next few months in a dispute over hours.
Members of the Rail, Maritime and Transport union (RMT) will walk out at midday on March 24 and 26, April 21 and 23 and May 19 and 21.
The union said around 1,800 of its members were involved in the dispute over the introduction of a compressed four-day working week.
Drivers had rejected the proposals in a referendum, said the RMT, amid concerns about shift lengths, unacceptable working time arrangements and the potential impact on fatigue and safety.
Eddie Dempsey, RMT general secretary, said: “London Underground is trying to force through major changes to working patterns that have already been rejected by our members.
“We are clear that these proposals raise serious concerns around fatigue, safety and work-life balance.
“Despite our best efforts over many months, no satisfactory outcome has been reached so we have no choice but to call strike dates.
“There is still time for London Underground to come up with a workable solution but we will take strike action if we cannot get a negotiated settlement.”
A Transport for London spokesperson said: “We shared our proposal for a four-day working week with our trade unions last year. Since then, we have been engaging with them on how best to implement the new working pattern.
“We have started talking with our unions about how to implement a four-day working week for train drivers on the Bakerloo line only.
“These threatened strikes are completely unnecessary and will have a serious impact on London’s businesses and commuters and we urge them to call off this action.
“The changes would be voluntary, there will be no reduction in contractual hours and those who wish to continue a five-day working week pattern will be able to do so.
“These changes will help us to improve reliability, improve our ability to flexibly deploy our drivers and enable us to offer a modern and efficient service while creating no additional cost.”