A three-day strike by 2,000 London Underground maintenance workers is to go ahead from Sunday after the failure of peace talks.
The Rail Maritime and Transport union said its members employed by Metronet will walk out at 6pm on Sunday after several days of negotiations ended without agreement.
The union also announced that the workers will start an indefinite overtime ban from April 22.
The RMT said the strike by engineers responsible for maintaining two-thirds of the Tube network would have an "immediate and massive" effect on services.
The union is in dispute with Metronet over plans to transfer workers to the individual companies in the consortium, which officials fear will affect terms and conditions.
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.
"As a result, the 72-hour strike scheduled for Sunday remains on, and the executive has today also given notice of an indefinite overtime ban to commence the following Sunday."
Metronet called on the RMT to cancel the planned three-day strike and continue talks aimed at resolving the dispute.
Mark Cooper, senior vice president, asset performance, said: "In recent weeks we have worked hard to reach an agreement with the unions. We remain available for talks at any time. The planned strike action will lead to disruption for the three million people who use the Tube every day. It is unnecessary and unwarranted."
