The Audit Office is looking into a DUP dinner hosted by North Antrim MP Ian Paisley at which Environment Secretary Michael Gove was the guest speaker.
It is understood to be focusing on £1,500 paid by Mid and East Antrim Council to sponsor a table at the dinner.
The event was attended by Conservative Minister Michael Gove.
The council insists the money was paid to Tullyglass Hotel, Ballymena, which hosted the dinner and not to the DUP.
In a statement, Audit Office officials said: "We... will specifically review that transaction as part of our audit procedures when we come to review the accounts."
The Electoral Commission announced it too was looking into the matter.
A letter leaked to the BBC revealed Mr Paisley asked the council to make a cheque payable to the hotel but to send it to the DUP offices in Ballymena.
Under Electoral Commission rules, councils are not considered "permissible donors" and donations received from such bodies must be returned within 30 days.
The commission is assessing the information which has recently come to light before deciding whether or not to launch a full investigation.
If the commission finds there are grounds for a full investigation, it could end up with the money being returned to the council.
The commission might also decide there is no case to answer as the DUP continue to insist the event was not a party fundraiser.
"We are aware of this matter and are considering it in line with our enforcement policy," said the commission.