A photo has emerged of DUP MP Sammy Wilson not wearing a face mask on public transport in London.
It appeared on social media on Thursday morning, showing Mr Wilson reading a magazine, as he headed to the airport.
A witness claimed he did not wear a mask for the duration of his tube journey from Westminster to Heathrow.
Mr Wilson told the Belfast Telegraph he only took it off briefly to answer a phone call.
Both the East Antrim MP and the DUP have not responded to requests for comment from BBC News NI.
The man who took the photo - who asked not to be named - said Mr Wilson got on the tube at Westminster at about 08:30 BST and sat opposite him.
He claimed Mr Wilson did not wear a mask during the journey.
But the DUP MP told the Belfast Telegraph newspaper: “I wore a mask before getting on the train, while on the train, in the airport and on the plane.
“I took a call and you can’t talk through a mask as you are muffled, so I took it off but put it back on again soon after.”
He said there were others in the carriage not wearing a mask.
Alliance deputy leader and North Down MP Stephen Farry later tweeted a photo of himself wearing a mask on the underground and said “most NI MPs do acknowledge, understand and respect rules” around face masks on public transport.
Transport for London says those caught not wearing a mask could face a minimum fine of £200, which doubles each time a person is caught, up to £6,400.
Exemptions apply for age, health and disability reasons and TfL provides an “exemption card” for those unable to wear one.
Mr Wilson has previously criticised the rules around wearing face masks.
In July, before face coverings in shops became mandatory, he posed on Twitter at an ice cream parlour in Islandmagee, County Antrim.
His message was “Support Local Business” and he went on to point out that “you can’t eat ice cream when you’re muzzled!”
He has also been critical of the government’s handling of the pandemic and on Wednesday, he criticised what he called the “scare tactics” being used by Downing Street in relation to Covid-19 statistics.