More than 150 maskless commuters in London were handed £200 fines in just one day, as compulsory face coverings were reinstated.
Face coverings become mandatory again on public transport amid rising concerns about the Omicron variant of Covid-19.
Some 152 people in London were fined on the day the rule was brought back, according to Transport for London (TfL).
This means a total of £30,400 in fines was issued in one day.
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.