The congestion charge will rise to "at least £6", Ken Livingstone has said.
Londoners will be consulted on the charge rise
The Mayor of London told BBC London on Monday that the £5-a-day toll will increase by at least £1.
He said: "I don't like putting up taxes and fares. I have always said that during this term it will go up to at least £6. "
He later added no final decision would be made until Londoners had been consulted. The new fare could be in place by early December.
He added: "You put it up the minimum you need to, to do what you have got to do. It won't be less than a pound."
The congestion charge will be put on hold between Christmas and New Year to help boost business.
The toll will be suspended on the three working days between 25 December and 3 January.
A recent report by Transport for London found by 2010 congestion will increase by 8% and carbon dioxide emissions are also set to increase, suggesting the road toll is failing to reduce traffic.