DUP MP Ian Paisley has strenuously denied newspaper claims that he did not declare trips paid for by the Sri Lankan government.
The Daily Telegraph alleged that in 2013, the prominent unionist MP accepted two all-expenses-paid trips for him and his family to the Indian Ocean Island, alleged to be worth a total of £100,000.
Responding on Twitter, Mr Paisley denied the allegations made in the story and said he would submit himself to the scrutiny of the parliamentary watchdog.
The House of Commons Code of Conduct states that MPs must declare any visit to a destination outside the UK which "relates in any way to their membership of the House or to their parliamentary or political activities" and which cost more than £300, unless they have paid for it themselves or out of parliamentary or party funds.
The rules state the MPs do not have to register family holidays, so long as they are "wholly unconnected with membership of the House or with the member's parliamentary or political activities".
Entries in the Register of Members' Interests should cover the cost of travel, hotels, meals, hospitality and car hire, and repeat visits should be registered if their combined value comes to over £300.
Mr Paisley's Register entries include a trade mission to Sri Lanka in 2012, as well as a second trip to the island that year as part of a cross-party parliamentary delegation examining post-war reconstruction, funded to the tune of £3,200 by the Colombo government.
There is allegedly no mention of the alleged trips in 2013.
Complaints over alleged breaches of the Code are investigated by the Parliamentary Standards Commissioner Kathryn Hudson, who reports to the Commons Standards Committee.
This committee, made up of MPs and lay members, has the power to recommend sanctions such as requiring an apology or temporary suspension, subject to a vote in the Commons.
Mr Paisley tweeted a picture of a letter from his legal representative, prominent libel lawyer Paul Tweed.
It said, "My client totally denies the defamatory inferences arising from the article in today's Daily Telegraph, including those relating to his registration obligations as an MP.
"He has now referred this matter, and a full explanation, to the Parliamentary Commissioner for Standards."
His party, the DUP, released a short statement saying confirming Mr Paisley would "rightly refer himself to the Commissioner for Standards", adding, "We await the outcome of that investigation".
Yesterday he was in his own constituency welcoming Prince Harry on a royal visit to Ballymena.
Today he finds himself at the centre of a controversy he strenuously denies.