Crucial talks are being held today in a bid to avert a planned 48 hour strike by London Underground workers.
Members of the Rail, Maritime and Transport union are due to walk out from 9pm on Saturday, February 6, in a dispute over ticket office closures, jobs and rosters.
The union said if talks with the company fail, the row will be referred to the conciliation service Acas.
RMT general secretary Mick Cash said: "The union demands to LUL on its Fit for the Future Stations programme are simple - no imposed rosters, no short notice duty changes and no imposition of new framework agreements.
"RMT will be attending the talks but with the clock ticking we are making it crystal clear that if there's any dragging of heels we will be calling for an immediate reference to Acas.
"With surging Tube demand, and against a background of chronic overcrowding, the union cannot and will not sit back while safety-critical jobs, that are the eye and ears of the service, are ripped away from our stations."
The dispute is separate from one which has delayed the start of an all night Tube service.