The planned resumption of Night Tube services this weekend is set to be affected by strike action from London Underground drivers over working conditions.
Members of the Rail, Maritime and Transport (RMT) union will walk out in a dispute over new shift patterns.
The union said their members are being asked to work both night shifts and day shifts after dedicated night staff were axed.
A 24-hour strike on Night Tube lines – Central, Jubilee, Northern, Piccadilly and Victoria – will start at 4.30am on Friday, with further walkouts planned in the coming weeks.
Transport for London warned of disruption to services and advised people to check before travelling.
RMT general secretary Mick Lynch said: “This strike is about the ripping apart of popular and family-friendly agreements that helped make the original Night Tube such a success.
“Instead the company want to cut costs and lump all drivers into a pool where they can be kicked from pillar to post at the behest of the management.”
He said the union had made several efforts to resolve the dispute with London Underground.
He added: “This strike action, and its serious consequences in the run-up to Christmas, was avoidable if the Tube management hadn’t axed dedicated Night Tube staff and perfectly workable arrangements in order to cut staffing numbers and costs.”
Nick Dent, director of London Underground customer operations, said: “The RMT’s planned strike action is needless and it will threaten London’s recovery from the pandemic, despite no job losses and more flexibility and job certainty for drivers.
“While every other union has agreed to these changes and our staff have been enjoying the benefits of the changes since August, we’re willing to work with the RMT and review the changes after Night Tube services have returned.”
The Night Tube has been suspended because of the pandemic and is due to restart on Friday.