Boris Johnson could be forced by the government to rethink his decision to scrap the western extension to the Congestion Charge zone in a row over air quality.
Following a public consultation the mayor announced last year that he would be scrapping the controversial scheme.
He also suspended the third phase of the Low Emission Zone, saying it could hurt businesses in the capital.
But now it has emerged that the government could force the mayor to either reconsider the move or come up with alternative schemes to offset any detrimental effects to air quality.
The Department for the Environment, Food and Rural Affairs is concerned that if strict European directives on pollution are not met the taxpayer could be fined up to £300m.
Defra can use its powers, as laid out in the Greater London Authority Act 1999, to force the mayor to come up with alternative schemes to improve air quality.
If enacted, it would be the first time government has used these powers to challenge the London mayor and means that ministers could force Mr Johnson to reverse policies if they clash with national decision-making.
A Defra spokesman said: “The Mayor has a duty under section 362 of the Greater London Authority Act 1999 to prepare and publish an air quality strategy. The current strategy was published in September 2002.
“The Mayor will produce a first draft of an updated air quality strategy in the summer and we look forward to receiving that.
“Regulation 30(2) of the Air Quality Standards Regulations 2007 would allow the Secretary of State to direct the Mayor to implement alternative measures to meet the air quality limits set out in the directive.”
Simon Birkett, from the Campaign for Clean Air in London, said that the government may have no option but to force the mayor to come up with stricter air quality measures.
“The government is obliged to meet these health standards so we are left with a political stand-off," he said. "What it looks like is that the government does have the powers to override the mayor."