Passengers could be prohibited from travelling on Tube trains and buses in London without face a covering, Sadiq Khan has announced.
The capital's mayor revealed he hopes to persuade the Government to change its position on the issue, but he has the option to "make it mandatory in London only".
Existing guidance from Transport for London only goes as far as advising passengers to wear face coverings, which is in line with nationwide policy.
Mr Khan told the London Assembly: "Next week I'll be considering whether I need to use the option I've got to make it mandatory."
He said he will lobby the Government in a bid to "reach a sensible compromise", as he noted that some train services in London are not under his control.
"We don't want confusion," he explained. "When there is a crisis, what's important is to have message clarity."
Mr Khan went on: "I leave the option available, which is to make it mandatory in London only.
"But I'm hoping we can persuade the Government to do the right thing."