“I didn’t have a mask on, should have had it on and am offering no excuse but it is sad that we have now become like East Germany under the Stasi where members of the public think it is acceptable to act as snoops,” he said. “Whoever took the picture didn’t approach me or say anything to me which I suppose would have been the proper way to behave.”
Earlier this week, Conservative MP Danny Kruger apologised after being spotted without a mask on a train in London. He said he “simply forgot” and also suggested he should have been approached quietly.
Twitter user James, who posted the photo of Mr Wilson reading a magazine on the Tube, has been retweeted 1,400 times and liked 3,400 times.
His tweet read: “Sammy Wilson MP on tube in London this morning with no mask after a £200 fine announced earlier this week. Disgrace. Rules not apply to MPs??”
DUP leader Arlene Foster said everyone is “equally subject to the law” after the issue was raised at a Stormont Executive press conference. She said: “Sammy has made a statement in relation to that matter.
“But just for clarity, I want to say this as clearly as I can, everyone is subject to the law, everyone is equally subject to the law and equal under the law.
“So it is important that we remember that, and that is the position of the DUP.”
She added that she had not had the opportunity to speak to Mr Wilson about the matter yet.
“Everybody has to abide by the law and take the consequences as well as not abiding by those laws,” she said.
Those caught not wearing a mask on public transport in London can face a £200 fine, which doubles each time a person is caught, up to £6,400.
There are exemptions for the rule on the basis of age, health and disability reasons.
Mr Kruger, David Cameron’s former speechwriter, said in a statement: “I boarded an almost empty carriage at Hungerford and quite simply forgot to put on my mask.
“When I got to Paddington I realised my mistake and covered up for the rest of my journey.
“If the person had reminded me rather than taking a photo and posting it on social media I would of course have put on my mask then and there.
“I do apologise for my mistake.”
Mr Wilson has previously been outspoken about the wearing of face coverings.
In July he tweeted a photograph of himself in an ice cream shop in Co Antrim not wearing a mask, with the message “you can’t eat ice cream when you’re muzzled!”
Face coverings in indoor places became compulsory in Northern Ireland on August 10.