MP Ian Paisley is referring himself to a parliamentary watchdog over claims he did not declare £100,000 in hospitality from the Sri Lankan government.
A newspaper report said the DUP and his family took two all-expenses-paid holidays to the island in 2013.
The Daily Telegraph said he recently met Sri Lankan officials to discuss the possibility of post-Brexit trade deals with the south Asian country.
But the MP said the report was “devoid of fact or logic” and “defamatory”.
On social media, Mr Paisley said he had referred the matter to his lawyer.
A DUP spokesman said: “Ian Paisley MP will rightly refer himself to the [Parliamentary] Commissioner for Standards.
“We await the outcome of that investigation.”