London Underground workers will stage a 24-hour strike in a dispute over the firing of a colleague, the RMT union has said.
Tube workers will walk out from 10pm on 7 May.
The union claimed one member of staff was sacked and two others disciplined for "intervening to stop a serious assault by a fare-dodger" last year.
Its executive instructed members at London Bridge station not to book in for shifts, service ticket machines or challenge passengers without valid tickets between 10pm on 7 May and 9.59pm the following day.
RMT general secretary Mick Cash said: "This was a shocking, violent incident and those that bore the brunt of it should have been supported and commended by the company. Instead they have been sacked or disciplined in what is the most appalling multiple miscarriage of justice."
Transport for London has been contacted for comment.
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