Sadiq Khan is set to suspend the Ulez charge later this year along with the Congestion Charge - but Londoners will only be able to get away without paying for one day.
Since August 29, anyone driving within Greater London is required to pay a £12.50 daily fee if they drive a non-compliant vehicle.
However, the London Mayor will suspend the charge for 24 hours on Christmas Day.
Families will be free to travel to visit relatives for the day without having to worry about paying the fee.
WATCH: The hidden costs of Ulez expansion
The majority of people who will benefit from the suspension are those who drive pre-2005 petrol and pre-2015 diesel cars.
Charges will be reimposed from midnight, meaning anyone planning to travel late could get caught needing to pay if they are still in the car after 12am.
Despite Ulez and the Congestion Charge being suspended, the low emissions zone (LEZ) operates all year round.
On Christmas Day the charge will be in force as usual.
Anyone driving after midnight will still be forced to pay the Ulez fee
PATransport for London says: "The Ultra Low Emission Zone (Ulez) operates 24 hours a day, every day of the year, except Christmas Day (25 December).
"The Low Emission Zone (Lez) operates 24 hours a day, every day of the year, including weekends and all public and bank holidays.
"Charging days run from midnight to midnight.
"If you drive within the Ulez area across two days, for example before midnight and after midnight, you need to pay two daily charges.
"The Congestion Charge covers central London. The Ulez operates across all London boroughs, and the M25 is not in the zone.
"The charges only need to be paid if you drive your vehicle within the zone. Parked vehicles are not subject to any charges."
Sadiq Khan has faced intense pressure in recent months over his decision to expand Ulez to cover all London boroughs but defended his decision alst week, describing it as necessary.
"The decision to expand the Ulez to outer London was a difficult one, it wasn’t an easy one, but it’s the right thing to do," he said.
"We’ve seen the benefits in central London, with almost a 50 per cent reduction in toxicity, a third fewer children being admitted to hospital with air pollution illnesses.
"In inner London, a 20 per cent further reduction in toxicity, 500 schools have children breathing cleaner air.
"I think breathing clean air is as important as drinking clean water. I think it’s a right, not a privilege. That’s why I want those in outer London to benefit as well."