Sinn Féin has criticised Belfast International Airport over its involvement in a Democratic Unionist Party (DUP) event in County Antrim.
Its chairperson Declan Kearney said the airport needed to clarify its role in the DUP's annual North Antrim constituency dinner in Ballymena.
At the event on Friday, DUP MP Ian Paisley interviewed former Conservative minister Priti Patel about Brexit.
Mr Kearney said he was concerned about transparency on the event sponsorship.
A spokesman for Belfast International Airport said it supports "all our political parties where it is clear the events they organise or are a part of are to the benefit of the airport".
In a letter to Mid and East Antrim Borough Council, a public relations firm said the airport was "sponsoring the dinner".
The correspondence said the council's participation "would add a significant dimension" to the evening, which would partly assess "the potential" of Brexit for business.
It did not state the event was a DUP dinner, but mentioned that Mr Paisley would "interview" Ms Patel.
Tables for 10 people cost £1,500.
The DUP MLA Paul Frew tweeted about the event, saying there had been "great support" at it, while MP Sammy Wilson said it was "great" to have "strong ally" Ms Patel in attendance.
'Partisan relationship perception'
Mr Kearney said a "huge issue of public interest" had arisen from what appeared to be "financial sponsorship by the airport for this DUP gala dinner".
Great to have my friend @patel4witham in Northern Ireland for the annual North Antrim DUP dinner. Priti is a strong ally as we continue the battle in Parliament to regain control of our laws, our money and our borders. pic.twitter.com/JHO5WOr8Dj— Sammy Wilson MP (@eastantrimmp) February 24, 2018
"The airport has enjoyed the political backing in the past from the [Northern Ireland] Executive," he said.
The airport's involvement in he event would mean "perceptions will arise about having a partisan relationship" with the DUP, he added, saying that he would write to the company that owns it.
"I intend to ask the owners of the airport whether they consider that it is tenable for one of their subsidiaries to be financially sponsoring activities of one political party."
Mr Kearney acknowledged that he had met the management of the airport "in the past".
Brilliant support for the Annual North Antrim DUP Dinner with guest speaker @patel4witham Priti Patel MP in @GalgormResort Ballymena. Great to have you here in the great Constituency of North Antrim Priti pic.twitter.com/0DAzOm4ele— Paul Frew (@paulfrewDUP) February 23, 2018
A DUP spokesman said: "All income and expenditure arising from the event will be handled in accordance with our rules and regulatory obligations."
The airport's spokesman said it is privately owned and does not receive government subsidies.
He also said it is campaigning for the removal of air passenger duty (APD) - a tax on the majority of flights from Northern Ireland - and "that means engaging with senior government figures to get our points across".
"We will continue with our efforts to remove APD and to engage with all politicians from whatever party to achieve that objective," added the spokesman.