Union leaders warned today of huge cuts on London Underground as a result of the Government's clampdown on spending, saying that a row over 800 ticket office job losses could be the "tip of the iceberg".
The Transport Salaried Staffs Association (TSSA) spoke out after obtaining a memo to staff from Transport Commissioner Peter Hendy warning of the "very significant effects" of the Government's spending review.
Mr Hendy said the Treasury had asked all non-protected Government departments to set out what budget cuts of 25% and 40% up to 2014/15 would mean for their spending.
"All departments affected, including the Department for Transport which provides some £3 billion a year of our funding, have now submitted their projected cuts to the Treasury based on these scenarios.
"Discussions between departments and the Treasury will continue over the summer, before the Chancellor makes his announcement on 20 October about where the cuts will actually fall.
"Notwithstanding the work we have been undertaking to mitigate the impact, we are faced with having to sustain a considerable reduction in our funding," said the memo.
Mr Hendy warned that London was the engine room of the UK economy and ill thought-out cuts would "seriously impede" the country's economic recovery.
TSSA general secretary Gerry Doherty said: "If TfL lose anything like £1 billion from its budget, the ticket office cuts will just be the tip of the iceberg.
"We could be looking at two or three times that amount because TfL have already halted all capital spending."
The TSSA and the Rail Maritime and Transport union are balloting their members on industrial action over the ticket office job losses and Mr Doherty warned that strike ballots would be called to halt any new threat to jobs in the autumn.
A TfL spokesman said: "The Mayor and TfL continue to make a powerful case for ongoing investment in London's transport network, including the Tube upgrades, Crossrail, a frequent and extensive bus network and sustainable transport, such as cycling schemes. This is being supported by business and a range of other stakeholders.
"Investing in the capital's infrastructure is vital not only to London but, as the motor of the UK economy, to the country as a whole.
"As our £5 billion savings programme demonstrates, we are also fully committed to delivering improved value for money for the fare-payer and taxpayer.
"It makes sense, therefore, to review our organisational structure as part of our ongoing efficiency programme to ensure that we deliver key infrastructure projects and frontline services to customers in the most effective way.
"The review will be undertaken by a team drawn from TfL staff, not consultants, reporting to the Commissioner and will take some months to complete. We will be working closely with our staff and trade unions throughout this process."