Around four out of five passengers at major railway stations are complying with the rules on face coverings, according to Network Rail.
The Government-owned company said the figure was based on anecdotal evidence from its staff at stations.
Network Rail manages 20 stations in England and Wales, such as Birmingham New Street, Manchester Piccadilly, Edinburgh Waverley, Glasgow Central, Leeds and 11 in London.
From Tuesday people across the UK have been required to wear face coverings on public transport and in shops, unless exempt, amid rising concerns about the Omicron variant of Covid-19.
Police and Transport for London (TfL) have enforcement powers for the masks rules, including the ability to issue fixed penalties of £200 for first-time offenders.
The amount is doubled for repeat offences, up to a maximum of £6,400.
Transport workers are not required to wear a face covering, with the exception of instructors and examiners providing driving lessons or tests.
TfL said 152 people in London were ordered to pay a £200 fine on Tuesday.
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.
The Rail, Maritime and Transport union (RMT) previously raised concerns that rail 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.