London Underground drivers are to stage a series of 24-hour strikes in a long-running dispute over working arrangements, the Rail, Maritime and Transport (RMT) union has announced.
A series of walkouts will begin on 26 November, with further strikes planned for 17 December, 19 December, 4 January, 6 January, 17 February, 23 February and 25 February.
The action will be taken in opposition to Transport for London (TfL) plans to introduce changes to conditions, which would include a four-day working week.
The union says drivers will face longer hours driving trains and work longer days, but TfL said the change would be voluntary and would mean drivers work fewer hours overall.
A series of strikes in the spring over the same issue caused significant disruption across the network, with some lines being entirely closed.
Despite further talks being held since, RMT has not accepted TfL's proposals.
General secretary Eddie Dempsey said: "London Underground is attempting to dress up a wholesale attack on drivers' working conditions as a voluntary four-day week.
"Our members are being asked to spend more time driving trains, accept longer and more unpredictable shifts and surrender agreements that have been negotiated and defended over many years."
The union also said it believed the changes would "pave the way for hundreds of job cuts".
TfL said that drivers choosing to remain on a five-day week would be given a guarantee of remaining at the same depot.
Nick Dent, director of customer operations for London Underground, said: "This will give our colleagues a real, meaningful choice on their working pattern without having to change where they work.
"This will also mean less time at work for Tube drivers, while delivering a more efficient, reliable Tube service for our customers."
BBC London's transport correspondent Tom Edwards said the issue of a four-day working week had turned into a "long-running, festering dispute".
"The RMT union regards it as an intensification of the job; TfL sees the changes as being minor and part of a good deal.
"The RMT has been here before and strikes have been called off before. But this is a knotty issue and patience is wearing thin."
About half of the drivers on the network are members of the RMT union.
Many others are represented by the Aslef union, which said it was "surprised" by the action.
Finn Brennan, Aslef's full-time organiser on London Underground, said: "The voluntary four-day week gives Tube train drivers an extra 35 days off every year with rosters based on a 34-hour week in return for some changes to working conditions and moving to electronic, rather than paper-based, systems for booking on for duty.
"Management have agreed that anyone who wants to keep working a five-day week will be able to do so without suffering any detriment, and we will be holding them to that.
"A strike designed to stop people having the choice of a shorter working week and more time off is a strange choice to make."
Under the proposals, most drivers would see their working week reduced from 36 hours to 35 hours, according to TfL. Their contractual hours would remain the same because paid meal breaks would be introduced.
This effectively means drivers would work longer days, but fewer days each week and fewer overall hours each week.
The RMT instead wants a 32-hour week over four days, meaning drivers would work three fewer hours each week for the same salary.
This is a long running, festering dispute.
RMT Union want a 4 day week but the question for the union is at what cost.
The Union says that hard won agreements over terms and conditions would be scrapped if they agreed.
It also says drivers who don't switch to a 34-hour 4 day week would also have to sign up to the new terms.
For example it would mean only 24 hours notice for changes to cover shifts, earlier start and finish times and less time to carry out other duties apart from driving. So drivers would actually spend more time in the cab then they do now.
The RMT union regards it as an "intensification of the job".
Tfl regard the changes as minor and part of a good deal.
Aslef the train drivers union have agreed.
The RMT Union has been here before and strikes have been called off before. But this is a knotty issue and patience is wearing thin.
The business group BusinessLDN said the strikes were likely to affect the hospitality sector in particular in the run-up to Christmas.
"These strikes will not bring any festive cheer to Londoners and visitors who rely on the Tube to get around the city," transport programme director Ed Richardson said.
"We urge both sides to reach an agreement urgently and avoid these damaging strikes."
