On Tuesday the RMT said industrial action will hit the majority of the capital’s train services when workers walk out for 24 hours on August 19.
Underground staff have been locked in a dispute over pensions and jobs with TfL, while Overground union members, employed by Arriva Rail London, are set to strike over pay.
The RMT said TfL had refused to share details of the government’s “final” draft funding proposal, which City Hall has until tomorrow afternoon to accept or reject.
The union added it did not receive assurances from the transport provider that there would be no reduction in jobs or detrimental changes to pensions and working conditions by its deadline on Tuesday.
Arriva Rail London members rejected a 5 per cent pay rise.
More than 40,000 union members at over a dozen train companies are also set to strike on August 12, 18 and 20 in a dispute with Network Rail over pay.
RMT general secretary Mick Lynch said: “This strike action by our members on London Underground and the Overground is yet another demonstration of how transport workers refuse to accept a raw deal.
“TfL have had ample opportunity to be transparent about the funding they will receive and to give tube workers the assurances they need.
“Yet they have totally failed to give those guarantees.
“And Arriva Rail London, a company swimming in money, refuses to give our members a pay rise that will deal with the escalating cost of living crisis.
“There will be significant disruption on the August 19 but TfL and Arriva Rail London bear responsibility for this break down in industrial relations.”