Fewer than 0.1% of people stopped by police for not wearing masks on trains received a fine, figures have revealed.
British Transport Police (BTP) said it stopped 14,726 people from 15 July to 15 August for failing to comply, resulting in 14 fixed penalty notices.
The rules, introduced in June, state anyone travelling on public transport must wear a face covering.
BTP said enforcement in the form of fixed penalty notices was only used as a “last resort”.
It said, from 30 July to 8 September, officers recorded 50,729 “interventions” with passengers not wearing face coverings, with 3,545 – 7% – of those told to leave the train.
The figures, obtained through a Freedom of Information request, showed 37 fines had been issued between 15 June and 14 July. BTP said it did not hold complete data for how many people were stopped during that time.
The rules have led to rows on public transport, with some spilling over into violence.
Last month, police said a train passenger was head-butted to the floor and repeatedly punched in the face for asking a fellow passenger to wear a face mask on a service between Slough and Langley in Berkshire.
And in Bournemouth, a bus driver was hit over the head and kicked on the floor for refusing to let a man board without a face covering.
Politicians have also been photographed breaking the rules.
Conservative MP for Devizes, Danny Kruger, apologised for forgetting to put on his face covering for a train journey from Hungerford to Paddington.
DUP MP for East Antrim, Sammy Wilson, was also caught on camera by a fellow passenger on the London Underground without a mask.
Mr Wilson said he accepted he “should have been” wearing a face covering and he would “accept whatever consequences there are”.
A BTP spokesman said: “British Transport Police has been working with rail industry staff since face coverings became mandatory on public transport in England on 15 June 2020 to engage with passengers, explain the importance of preventing the spread of the Covid-19 virus and encouraging people to wear face coverings.
“Enforcement, in the form of fixed penalty notices, has only been used as a last resort.”
Rail campaign group Railfuture said it was difficult to strike a balance but said BTP had got it “about right”.
Spokesman Bruce Williamson said: “We want a safe railway. We do not want to deter people from travelling.
“It looks like British Transport Police are doing this right. If fines are a last resort, it’s good, they are not being heavy-handed.”
BTP has jurisdiction for the railway network in England, Scotland and Wales, which includes the London Underground, Docklands Light Railway, Croydon Tramlink, Midlands Metro, Glasgow Subway and part of the Tyne & Wear Metro.