Dozens of maskless passengers have been fined as compulsory face coverings were reinstated.
Face coverings become mandatory again on public transport from Tuesday amid rising concerns about the Omicron variant of Covid-19.
Some 152 people in London were ordered to pay a £200 fine on Tuesday, according to Transport for London (TfL).
Another 125 were asked to leave TfL services, and 127 were prevented from boarding a service or entering a TfL station.
Meanwhile TfL said its staff reminded more than 5,100 people to cover their faces on its bus, Tube and rail network.
You must wear a face covering on all our services unless exempt
Our officers will continue enforcing the requirement, including reintroduction of powers for TfL and police to issue £200 fines for first offence
— Transport for London (@TfL) November 30, 2021
The Rail, Maritime and Transport union (RMT) previously raised concerns that train workers would be left to deal with angry passengers who do not want to wear face masks.
General secretary Mick Lynch said on Sunday that more resources were needed to police the use of face coverings.