Off-peak Tube and train fares all day on Fridays will be trialled by Transport for London (TfL) in a bid to boost passenger numbers and support the capital’s economy.
Sadiq Khan has asked TfL to launch a three-month trial in March.
He said the organisation’s usage data showed Fridays were quieter than any other week day.
Susan Hall, the Conservative mayoral candidate, said the trial would not make any difference.
TfL said that midweek Tube usage was at 85% compared to pre-pandemic levels and Friday usage was about 73%.
Mr Khan said: “London has really bounced back since the pandemic, but the lack of commuters returning on Fridays is a clear exception – with a major knock-on effect on our shops, cafes and cultural venues.
“That’s why I’ve asked TfL to trial off-peak fares on Fridays, and I encourage Londoners to get involved.”
Amit Patel, who works in a newsagent opposite Marylebone Train Station said their trade on a Friday had trailed off since the pandemic.
“We’ve got to make ends meet,” he said. “So we’ve just got to try and cope.
“It’s not anywhere close to what it used to be.”
Tom Edwards, BBC London transport correspondent
Go into a lot of ticket halls at 09:28 GMT and you will see travellers waiting for off-peak to start so they can get a cheaper fare.
There is no doubt, commuters are sensitive to fare changes.
Making Fridays off-peak is innovative. I can’t recall it happening before in the UK although other cities in Europe go much further and offer free public transport all the time.
Since the pandemic things have changed and working from home has killed off Fridays in the office for many and London’s transport is much quieter. The mayor hopes this will bring them back.
The big question is will this cost Transport for London lost revenue or will returning numbers make this revenue neutral? And will saving a few pounds be a big enough of a draw for those at home on a Friday?
Also it looks like the practicalities still need to be worked out with the train companies.
Politically, of course the context is a mayoral election looms in May. And the incumbent Labour mayor Sadiq Khan is trying to put the cost of living firmly on the agenda.
His critics and opponents will say this is nothing more than a cynical election bung.
Peak fares apply from 06:30 to 09:30 and from 16:00 to 19:00 on both TfL and National Rail services in London.
Ms Hall said commuters “might change their habits slightly” but the saving was not enough to make a major difference.
“If people are doing a three-day week [in the office], they’ll just change their days and not come in another day,” she said.
The announcement comes a week after Mr Khan said he was freezing TfL fares for another year from March.
Kate Nicholls, chief executive of UKHospitality, said the trial was “exactly the type of flexible approach needed to boost journey numbers and stimulate footfall”.
And Chris Hayward, City of London Corporation policy chairman called it a “welcome shot in the arm to our businesses”.
Rob Blackie, of the London Assembly’s Liberal Democrats, said: “It’s a great idea to cut fares on Fridays, when the Tube is less crowded. However ‘dynamic pricing’ has to be about using spare capacity.
“Any dynamic model must only offer discounts for travelling during less periods or in less busy places.”
Zoë Garbett, the Green Party’s candidate said she welcomed any TfL fare cuts but added: “But this feels like a gimmick rather than something that will actually help many Londoners.”