Thousands of Transport for London staff are to be furloughed from Monday after fare income fell by 90%.
TfL said its main source of revenue had almost "disappeared" amid the coronavirus lockdown.
Some 7,000 staff whose work has already been reduced or put on hold will be affected.
Tube journeys have fallen by 95% and bus use by 85% after people were urged only to make essential journeys to stop the spread of COVID-19.
TfL will be able to access funding from the government's Coronavirus Job Retention Scheme, saving it around £15.8m every four weeks.
Under the scheme, firms can get funding to pay 80% of a worker's wages, up to £2,500 per month.
The staff affected affected, around a quarter of TfL's workforce, will be placed on furlough for an initial period of three weeks.
London's transport commissioner, Mike Brown said: "The transport network is crucial in the fight to tackle coronavirus and it will play a similarly vital role in supporting the country's economy as it recovers from the pandemic.
"We have significantly cut our costs over recent years but nevertheless the success of encouraging the vast majority of people to stay at home has seen our main revenue, fares, reduce by 90%.
"We are now taking steps to use the government's Job Retention Scheme to further reduce our costs where work has been paused because of the virus, while at the same time supporting our staff financially.
"Our work with the government about the support that we need are ongoing and are constructive.
"We hope for an urgent agreement so that we can continue to provide the city with the vital transport it needs now and going forward."