A series of Tube strikes linked to the collapse of a maintenance firm will go ahead, a union has confirmed.
The first 72-hour strike will start on Monday
Members of Unite, the Rail, Maritime and Transport (RMT) union and the Transport Salaried Staffs Association are due to begin action on Monday.
They are protesting over job losses faced by Metronet staff. Transport for London (TfL) said all issues raised by the unions were being addressed.
The strikes are planned to take place on 3, 4 and 10 September.
Further talks are due to be held on Monday before the planned industrial action.
The RMT said more than 2,300 of its members would walk out for 72-hours from 1800 BST on Monday.
Union leaders are seeking guarantees over jobs, transfers and pensions from Metronet which went into administration in July.
The RMT said the maintenance firm had failed to offer the "unequivocal" guarantees on jobs, transfers and pensions it was seeking.
London mayor Ken Livingstone told union members: "The Administrator and Metronet have written to you today giving you the necessary assurances that there will be no reduction in jobs or transfers of employees from Metronet during the period of administration and that your members pensions will be fully protected.
"I can confirm that no Metronet employees will lose a penny of their pensions."
He added: "This meets all of the concerns that you raised with me when we met and provides you with clear assurances that no Metronet employees will suffer loss of pensions, jobs or be transferred as a result of the collapse of Metronet.
"Under these circumstances the strikes called for 3 September should not proceed."
But Bob Crow, general secretary of the RMT, said a letter from Metronet and the administrator fell "way short" of the guarantees workers deserved.
"The only assurances we have received about jobs and transfers cover only the period of administration, and that is simply not good enough."
He warned of a second 72-hour strike on 10 September if the issue was not resolved.
Members of the Transport Salaried Staffs Association are also due to walkout for 48-hours on 4 September.