Ian Paisley has faced criticism for billing a charity nearly £6,000 to fly first-class to a New York conference.
The Democratic Unionist Party (DUP) MP was invited to an event marking 20 years since the Good Friday Agreement.
The bill was covered by Cooperation Ireland, according to Mr Paisley's register of interests.
Last year he was suspended from the House of Commons after failing to declare two luxury family holidays to Sri Lanka, paid for by its government.
BBC News NI understands that Mr Paisley accepted an invite to speak at the New York event at the last minute and was only able to be in the US only for a short time.
The Irish News reports that he later billed the charity £5,925 for first class flights and another £400 for a hotel.
Other high-profile speakers, such as the Irish foreign minister Simon Coveney, flew in economy-class, with flights more than 10 times cheaper.
It is also claimed that Mr Paisley's bill to the charity included the cost of a limousine service to the airport but he disputes that.
Colum Eastwood, the leader of the SDLP, has called on the North Antrim MP Paisley to pay back the money for the New York event.
It is the latest occasion about which Mr Paisley has faced criticism about a lavish lifestyle.
Last year, he was suspended for 30 days from the House of Commons after failing to declare luxury holidays paid for by the Sri Lankan government, which he later lobbied on behalf of.
Calls have been made for the Westminster standards committee to investigate a complimentary holiday he received at a luxury Maldives resort after advocating on behalf of its government.
Mr Paisley said he paid for part of the holiday and the rest was paid for by a friend.
He did not reveal the identity of this friend.
He said the friend was not connected to his work and has received no benefit as a result of his work.