A working party has been set up to investigate running Tube services for 24-hours a day during the 2012 London Olympics.
Union sources said they expected a battle over pay rates for round-the-clock working by thousands of London Underground staff during the Games, which run from July 27 to August 12.
Hundreds of thousands of extra visitors are expected to be in the capital for the Olympics, placing an extra strain on the transport system, including the Tube, which is used by more than three million passengers every day.
It is understood that the working party has been set up between Transport for London (TfL) and the Rail Maritime and Transport union and Transport Salaried Staffs Association.
Union sources said they had already ruled out a two-year deal from this April, to include the period covering the Games.
The unions are still in dispute with TfL and London Mayor Boris Johnson over 800 ticket office job losses, which sparked a series of strikes last year.
RMT general secretary Bob Crow said that despite “a campaign of spin from Transport for London and Boris Johnson suggesting that all is sorted, the hard fact is that there is no agreement with the unions in place for operating hours, volume of service, staffing levels or payments for next year's Olympics”.
“Not only that, but the continued job cuts and attacks on maintenance schedules mean that the Tube is short of capacity and prone to regular breakdowns at the best of times, let alone when we've got another million people to shift around the City.
“None of this is helped by Boris Johnson's continued refusal to actually sit down and talk directly with the transport unions on the crucial issue of the cuts programme being driven by his senior officials.
“It's clear, as we lurch from crisis to crisis, that the Mayor can't keep London moving now, let alone for the Olympics in 2012, and his refusal to even meet with the representatives of the transport workforce makes a mockery of all his claims about having a transport strategy in place,” Crow said.
A TfL spokesman said it is “on track to deliver all transport improvements well ahead of the Games and are confident of supporting a fantastic London 2012 Games and keeping London moving”.
“We are now drawing up our detailed transport plans for the Games. However, no decisions have yet been taken about the Tube's hours of operation during 2012,” the spokesman said.
A senior TSSA source said: "Boris played shamelessly to the Tory right during last year's ticket office dispute by deliberately provoking walk-outs by sacking staff without any sort of agreement.
"But we only regard it as half-time as far as pay and conditions are concerned.
"In the second half, with the Olympic wind at our backs, we expect Boris to be much more reasonable when it comes to rewarding loyal staff for working hard to ensure the success of the Games."
Meanwhile, the RMT said that a decision to switch maintenance of trains on the Jubilee Line from Alstom back in-house was the “final nail” in Tube privatisation.
TfL said the fleet maintenance work will move in-house from May so it can have full control over management and costs and was being implemented via a clause in Alstom's contract with Tube Lines, whose work is being taken over by LU.
A TfL spokesman said to ensure there is no disruption to customers during the transition, 115 staff currently employed by Alstom, which has maintained the fleet since 1997, will be transferred to Tube Lines, which is wholly owned by TfL.
“This will help London Underground to provide a full, reliable service to Jubilee Line passengers during an important period in the line upgrade when more trains are needed for the new timetable, and the entire fleet is due a maintenance overhaul. Alstom and Tube Lines will work closely to keep all staff fully informed during the transitional period.”
Crow said the “shambles at London Underground deepens by the day and for months Boris Johnson has presided over chaotic management, attacking RMT and our members and now he has the embarrassment of admitting through this private contract collapse that we were right and he was wrong”.
“Passengers have put up with months of chaos with some forced off trains and sent up tunnels as this contract has been allowed by Johnson and his officials to drag on. The collapse of this contract should be the final nail in the coffin of Tube privatisation.”