IAN Paisley billed a Belfast charity for almost £6,000 to fly first-class to a peace conference in New York.
Others travelling to the event from Ireland and Britain, including tánaiste Simon Coveney, flew in economy – more than 10 times cheaper in price.
Political opponents branded the DUP MP "truly shameless" for recouping the high-cost travel from a charity.
It is Mr Paisley's latest lavish trip controversy after months of criticism and parliamentary probes over holidays in the Maldives and Sri Lanka.
The North Antrim MP was a guest speaker at the '20 Years of Peace' conference in New York last year marking two decades since the Good Friday Agreement.
The event was organised by Cooperation Ireland, a registered charity aimed at encouraging north-south dialogue and peace-building.
Mr Paisley spoke on a panel alongside other high-profile figures including former US senator George Mitchell, former SDLP MP Mark Durkan and ex-Sinn Féin MP Pat Doherty.
Tánaiste Simon Coveney gave a speech at the event. He flew economy on budget airline Norwegian Air and his government department covered the cost, a spokesman said.
Other attendees were asked to pay their costs up-front and submit these later as expenses claims to Cooperation Ireland to recoup their money.
Mr Paisley's flights cost £5,925.11 and his accommodation was £402.23 – a total of £6,327.34. The cost was covered by Cooperation Ireland, according to his register of interests.
It is understood all other high-profile invited speakers from Ireland and Britain travelled in economy-class seats.
The SDLP said Mr Durkan flew economy from Dublin to New York with Aer Lingus, and Co-operation Ireland covered the cost.
Sinn Féin said Mr Doherty "did not fly first-class or business-class and stayed with relatives so no accommodation costs were incurred".
Irish News columnist Deaglan de Breadun, who chaired the session involving Mr Paisley, said he was on the same economy flight as Mr Coveney.
He was already planning a separate trip to New York before being invited to the conference, and had booked a return flight from Dublin at a cost of €283.74.
He said organisers reimbursed the full cost of the flight including a €100 rescheduling cost, as well as the bus fare between the airport and Manhattan, additional hotel costs and a food allowance.
Sinn Féin councillor Geraldine McAteer – who attended to take part in another panel discussion due to her role with West Belfast Partnership Board – said her flights were around £530, travelling economy with Aer Lingus from Dublin to New York.
The Belfast rep said her trip including accommodation cost around £1,040 and it was reimbursed by the charity.
Ms McAteer said the event in February was "really useful" and she considered it "an honour" to attend.
A first-class return from London to New York non-stop can cost around £4,000 to £6,000, according to online price comparison websites.
This compares to a cost of around £250 to £450 to fly the same round trip in economy class.
Cooperation Ireland did not wish to comment on specific invitees, but a spokesman said each person made their own individual arrangements and their expenses were reimbursed by the charity based in Belfast.
The SDLP's John Dallat criticised Mr Paisley for the scale of expenses charged to the charity.
"It takes a truly shameless public representative to accept luxury flights from a charity," the East Derry MLA said.
"This increasing trend by Ian Paisley Jr to travel in style – but not at his own expense – truly does strip him of the integrity that his office is befitting of."
Sinn Féin described the price of Mr Paisley's journey as "astonishing".
"Mr Paisley has a much-publicised penchant for travel at the expense of the taxpayer and others," a spokesman said.
"This includes the government of Sri Lanka which was guilty of the most horrific human rights abuses.
"Mr Paisley seems to believe that his role as an MP gives him a ticket to ride with lavish benefits and perks."
The DUP did not respond to requests for a comment.
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IAN Paisley's luxury travel at a charity's expense is the latest occasion the DUP North Antrim MP has faced criticism for his lavish trips abroad.
In July he received an unprecedented 30-day suspension from the House of Commons after failing to declare two luxury family holidays to Sri Lanka in 2013 paid for by its government, for which he later lobbied.
The MP had urged then prime minister David Cameron not to support a United Nations (UN) probe into human rights abuses on the south Asian island.
Mr Paisley's suspension prompted the first recall petition in UK parliamentary history, but the petition fell short of the 10 per cent of registered voters required to trigger a by-election.
In December he faced questions over receiving a complimentary holiday at a luxury Maldives resort some months after advocating on behalf of its government.
Mr Paisley, his wife and two sons received full-board five-night stay at the resort in 2016, some months after he was part of a controversial parliamentary visit to the islands – at a time when the Maldives government was being criticised by the UN and Commonwealth for human rights abuses.
A Westminster standards watchdog has been urged to investigate but Mr Paisley has denied any wrongdoing, insisting it was a private family vacation paid for by himself and a friend unconnected to his work.
Mr Paisley has also courted controversy recently for organising DUP dinners attended by senior Tories.
One event is being probed by the Electoral Commission after two councils paid a total of £3,000 for tables at the hotel function.
The watchdog, which is treating the payments as 'donations' to the North Antrim MP, is investigating because local authorities are not considered "permissible donors".
The councils have defended the payments, while the DUP has denied the event was a party fundraiser.
