Tube workers are to take part in a three-day strike next week as talks to resolve an employment row broke down.
The Rail Maritime and Transport (RMT) union said 2,000 of its members employed by maintenance firm Metronet would walk out from 1800 BST on Sunday.
The RMT also announced that the workers would start an indefinite overtime ban from 22 April. The row is over plans to transfer staff into parent companies.
Metronet has said any industrial action would be unjustified and unwarranted.
London Underground (LU) said the action would not bring the Tube network to "a standstill".
"The employees who may undertake industrial action are Tube maintenance workers working for Metronet, not Tube drivers or station staff", a spokesman said.
The dispute centres on plans to transfer around 250 staff to Bombardier Transportation to help introduce new trains and improve reliability.
Metronet senior vice president Mark Cooper called on the union to call off the strike and continue talks.
He said: "The planned strike action will lead to disruption for the three million people who use the Tube every day. It is unnecessary and unwarranted.
"We remain available for talks at any time."
Series of meetings
The RMT said the industrial action would have an "immediate and massive" impact on services.
General Secretary Bob Crow said: "We have had a series of meetings with Metronet this week but we have been unable to reach agreement.
"It is a great pity that after we suspended the overtime ban scheduled for this week to enable those talks to take place, the company has not taken the extra step towards us that could have resolved the dispute."
Metronet is responsible for maintaining two-thirds of the Tube network.
The strike will end at 1800 BST on Wednesday.