The Transport Salaried Staffs' Association (TSSA) has rejected a new offer on jobs from the London Underground in a bid to avoid a 24-hour strike.
The union said its members are going ahead with the industrial action from 6pm on Sunday.
It comes after the biggest rail union, the Rail, Maritime and Transport (RMT) union, walked out of talks at conciliation service Acas, yesterday. Talks between both unions and the London Underground had previously broken down on Friday afternoon.
The strike is expected to result in mass station closures, with TfL saying the majority of Zone 1 stations will be closed.
John Leach, regional organiser for RMT told reporters London Underground's position had not changed throughout the week. He said the unions wanted guarantees a "significant number" of staff will be hired to keep the lines safe, whereas, he added, "They've just offered us a band-aid on a gaping wound."
Steve Griffiths, London Underground's chief operating officer, said 150 extra staff would be recruited, adding, "This number is bound to increase as we work through the other areas that need to be addressed."
The action concerns a historic dispute between the unions and TfL that started under Boris Johnson over the closure of ticket offices at Underground stations.
Mayor of London, Sadiq Khan, said:
My message to the unions is clear: it is not too late to cancel this strike and get back around the negotiating table for the sake of all Londoners.
I have instructed TfL to continue negotiating and we will be available around the clock to resolve this dispute.
This strike is going to be a huge inconvenience to commuters, tourists and TfL staff. And it is pointless.
What will happen when the strike starts at 6pm?
Although National Rail services will not be affected by the strike, there will be no Tube running from key interchange stations like Victoria, King's Cross, Waterloo, Paddington, Euston, Bank and London Bridge.
There will be no service on the Victoria and Waterloo & City lines, and TfL said all other lines would be severely affected, with "limited services" in outer London.
Piccadilly line services will run between Hammersmith and Heathrow Terminals 1, 2 and 3 and DLR services will be running but may terminate before Bank station.
About 100 extra buses will be running and river services will be "enhanced".
More on TfL's Tube strike page, which will be updated once it has more information on how many members of staff strike.