Belfast International Airport is facing criticism for its alleged sponsorship of a DUP gala dinner.
The event, held at the luxury Galgorm resort on Friday, featured North Antrim MP Ian Paisley interviewing former Cabinet minister Priti Patel.
A letter sent to the local council said the airport was sponsoring the event but did not mention the DUP, other than a reference to Mr Paisley.
Tweets from party members about the event described it as the annual North Antrim DUP dinner.
An apparent failure to inform those invited of the party link was "seriously wrong", Mid and East Antrim Borough councillor Declan O'Loan said.
"For the airport to be the persons who were sending the invitation letter to the council while they were the sponsor of the event and not the organiser of the event, I think that to me is entirely unprecedented and I think it was wrong," he said.
"That letter of invitation to the council failed to disclose who was organising the dinner and I think that is seriously wrong.
"So I think in a number of aspects the airport have put themselves very much in the wrong place in relation to an event that turns out to be expressly party political."
Mr O'Loan said it was the second such event in the space of six months.
An event held in September and attended by Environment Secretary Michael Gove was described by the airport PR in the letter as "an excellent networking opportunity".
A table at Friday's event was priced at £1,500 for 10 people, the letter said, with a request that people pay the Galgorm directly.
Sinn Fein's Declan Kearney said the airport has questions to answer.
He said: "My concern relates to the transparency around the sponsorship and beneficiaries of this event.
"I will be seeking clarification from Belfast International Airport, which has enjoyed government backing, as to whether or not it directly or indirectly sponsored a gala dinner which DUP representatives have claimed was a DUP event."
He added that it is a matter of "acute public interest" to establish whether any of the money paid to attend the dinner would be transferred to the DUP.
A DUP spokeswoman said: "This was a DUP dinner organised by our North Antrim Association and understood to be the case by all concerned.
"All income and expenditure arising from the event will be handled in accordance with our rules and regulatory obligations."
Belfast International Airport said it is a privately owned company that supports all Northern Ireland's political parties "where it is clear the events they organise, or are a part of, are to the benefit of the airport".
A spokeswoman added that as part of their campaign to remove the airport tax known as Air Passenger Duty they will continue to engage with "senior Government figures to get our points across".
She said: "We will continue with our efforts to remove APD and to engage with all politicians from whatever party to achieve that objective."