Members of the Rail, Maritime and Transport union (RMT) on the London Underground are set to strike on Friday, August 19.
The strikes come over a long-running dispute over jobs and pensions as inflation rights soar across the nation.
The tube strikes will take place in between strike action at Network Rail and 14 train operators on August 18 and 20 as well as members of the Transport Salaried Staff's Association (TSSA).
RMT has said the strikes have been prompted by Transport for Londons (TfL) "refusal" to share details on government proposals regarding the funding of transport in the capital.
The union has said it has given TfL until August 2 to provide assurances over pay, pensions and job security.
RMT general secretary, Mick Lynch said: "Our members will once again take to picket lines in this important dispute over pensions, jobs and conditions.
“They have been messed around by TfL and mayor Sadiq Khan. And to add insult to injury, they have not seen the detail of this funding letter from government.
“Unless there can be assurances made about jobs, pensions and detrimental changes to working conditions, then our strike on 19 August will go ahead.”
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