Allowing driverless trains should be a condition of any future funding of Transport for London (TfL), Prime Minister Boris Johnson has said.
There are currently no driverless trains on the London Underground.
Train drivers' union Aslef dismissed Mr Johnston's call saying: “As always, Boris Johnson is talking nonsense about driverless trains."
"Slashing government funding to TfL means that they cannot afford the signalling upgrade and other technology that would be needed for driverless trains," a spokesman said.
On a visit to the site of a planned rail manufacturing facility Mr Johnson told reporters: "You can run these trains without the need for somebody to be sitting in the driver's cab the whole time.
"So what I will be saying to the London transport authority is let's take advantage of this technological leap forward, let's not be the prisoners of the unions any more, let's go to driverless trains and let's make that a condition of the funding settlement for Transport for London this autumn.
"That's the way forward for this country and we want to make use of the fantastic technology we've got and provide a better service for people in the capital and take the whole economy forward."
During his time as Mayor of London, Mr Johnson repeatedly predicted the introduction of driverless trains.
Between 2008 and 2016, Mr Johnson was involved in a series of bitter disputes with trade unions in relation to London Underground services.
Mick Lynch, senior assistant general secretary of the Rail, Maritime and Transport (RMT) union, said: "It is outrageous for Boris Johnson to wheel out the dangerous nonsense of driverless trains as a condition of the emergency Covid-19 funding of Transport for London.
"This is the sort of cheap political stunt that was a hallmark of his time as mayor and we would have hoped he would have grown up by now.”
Some trains on the Transport for London network are operated in semi-automatic mode, but are not driverless.
This means drivers still have to operate doors but they are not responsible for acceleration or braking unless problems occur.
TfL's Docklands Light Railway does not have drivers in cabs but uses onboard attendants who control the doors.