Essential upgrades to the Tube network could be stopped, the RMT said
"Significant scaling back" of essential upgrades to Tube routes by a contractor looking to save £2bn could hit jobs and the Olympics, a union has warned.
The Rail, Maritime and Transport (RMT) union said Tube Lines was in a "stand-off" with Transport for London (TfL) over revised terms of its contract.
Tube Lines said there were "financial constraints" but denied it would have an impact on projects or upgrades.
A TfL spokesman said "genuine proposals to work more efficiently" were welcome.
The RMT said Tube Lines was trying to cut £2bn from its estimated costs of £7.2bn over the next seven-and-a-half years.
RMT General Secretary Bob Crow said: "It is clear that there is a £2bn stand-off between Tube Lines and Transport for London on the works programme on the Piccadilly, Northern and Jubilee lines, with Tube users and Tube workers caught bang, smack in the middle."
He warned that Londoners could see another failure similar to Metronet, leaving taxpayers to "pick up the pieces".
"Meanwhile, jobs and essential works on these lines are left at risk in the run-up to the 2012 Olympics," he said.
A TfL spokesman said: "The restated contract terms we submitted to Tube Lines specify the scope of work they are required to deliver and include the line upgrades and track, stations and infrastructure renewals.
"We believe they are affordable.
"Should Tube Lines have any genuine proposals to work more efficiently and economically, and therefore reduce costs, then we would, of course, welcome that," he said.
A Tube Lines spokeswoman said the company, which has a 30-year contract with London Underground with terms reviewed every seven-and-a-half years, was aware of TfL's "financial constraints".
She said: "We have therefore also provided an alternative approach which would deliver all LU's key objectives, including the vital line upgrades, within a much lower budget."
Tube Lines is focusing on making savings by improving "working practices" and "greater efficiency" but denied the company was in any danger of collapsing like Metronet.
TfL and Tube Lines have another six months to finalise contract details.
The work of maintenance firm Metronet, which looked after nine lines, was taken over by TfL after it went into administration in July 2007.