Tube drivers have threatened to walk out later this month when the Night Tube service is due to restart.
The overnight service has been closed because of the coronavirus pandemic.
The Rail, Maritime, and Transport union (RMT) said its members will stage a series of strikes in a dispute over staffing.
Mayor of London Sadiq Khan wears a face covering as he travels on the Tube
Twenty-four-hour strikes will take place on the Central, Jubilee, Northern, Piccadilly and Victoria lines from 26 November and 18 December.
There will also be stoppages on the Central and Victoria lines between those dates.
RMT general secretary Mick Lynch said: “No one has worked harder to ensure a safe environment for women on London Underground than the RMT.
“While Tube bosses have axed staff and left stations routinely unstaffed, with all of the obvious risks, we have campaigned relentlessly for the front line, physical presence of visible staff on stations and platforms.
“We are now being repaid by the imposition of working arrangements that would wreck the work-life balance of our members.
“All of this 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.
“It’s that action which has led us to make today’s announcement.
“RMT supports the reintroduction of the Night Tube but we know full well that prior to its suspension during the pandemic it was a magnet for violent, abusive and anti-social behaviour.
“We warned months ago that slashing 200 Night Tube train driver positions would create a staffing nightmare and LU need to start facing up to that reality.
“The union remains available for talks.”
Nick Dent, director of London Underground Customer Operations, said: “We are disappointed that the RMT is threatening London with this unnecessary action.
“The positive changes to Tube driver rosters have provided greater flexibility for drivers as well as permanent work and job certainty, something welcomed by all other unions.
“We have been meeting with the RMT for a number of months through Acas to try and resolve their issues and we remain open to talking further.”
It comes as Uber announced it was increasing its London prices by 10% in an effort to attract more drivers. The company will also increase the cost of an airport journey during peak times by 25%.
An Uber spokesperson said: “We’re making these changes to help provide a better rider experience, by signing up more drivers to meet the growing demand.
“We know people rely on Uber to book a safe trip around London and this small fare increase will help reduce wait times. As always riders will get a fare estimate before booking their journey.”
The company will continue to take a 25% cut of taxi fares.
