London mayor Boris Johnson is considering raising the congestion charge by around £10 in a bid to curb air pollution.
The mayor wants a new Ultra Low Emission Zone (ULEZ) to be introduced by 2020 in order to help London meet EU limits for nitrogen dioxide.
Euro diesel engine standards have not delivered the emission savings expected, Mr Johnson claimed, and governments have been encouraging drivers to buy diesel cars.
The ULEZ would help to address these problems in a "reasonable way" and give motorists enough time to comply with the new standards.
Mr Johnson said: "Improving London's air quality is an urgent challenge, it affects the health and well-being of all Londoners, and it simply cannot be put on hold."
The levy would come on top of the congestion charge, which is imposed on cars driving into the centre of the capital.
Only diesel vehicles meeting the Euro 6 emissions standard would be exempt, while owners of petrol cars registered before 2006 would be required to pay.