The Electoral Commission is to review a council's failure to disclose a DUP mayor's clothing expenses ahead of local government elections.
Government transparency watchdog the Information Commissioner's Office has also confirmed it is probing Mid and East Antrim Borough Council.
It follows a long-running controversy over Audrey Wales' more than £2,300 clothing bill she racked up during her time as mayor.
Read more: Far-right group submits complaint to PSNI against ex-Belfast councillor
When asked under Freedom of Information laws in 2019 shortly before an election about the expenditure, the council claimed Ms Wales had only spent £190.
The councillor said she had sent a cheque at the time reimbursing her council for most of the spending to stop "electorally motivated questions".
The cheque was received by the council's then chief executive Anne Donaghy - but it was never cashed.
Ms Wales, who sent a second cheque in 2021 after learning the first had not been processed, insisted that "at all times" she acted in line with "guidance from council officials".
In January last year, the council commissioned Belfast-based firm ASM to examine the controversy.
The report was completed in April and the council refused to publish it, but a copy was leaked to the Belfast Telegraph.
The 73-page report found the council's FOI response had been "inaccurate" and involved "a deliberate manipulation".
It said the election "appears to have had a significant impact on the decision" to withhold the FOI response until after polling day.
The delay was "highly inappropriate and prima facie this appears to have been an attempt to subvert and delay the FOI process".
It added: "Any attempt to influence the electoral vote could in our view also be a matter for the Electoral Commission."
The report also noted "contradictory" accounts about the cheque not being cashed.
It said it was "clear that a cheque was written, was in the chief executive's possession for a period of time, was never cashed and cannot now be located".
Ms Donaghy denied being involved in discussions about the FOI and said an email she sent referring to the cheque showed that she intended to cash it.
Former UUP councillor Stephen Nicholl said he has written to the Electoral Commission and has asked the council to send the body a copy of its internal report.
In his letter, he asked the commission to review the report and "consider what further protections are required to restore confidence in the democratic process".
Mr Nicholl lost his seat in Ballymena in a close-run council election in 2019, in which Ms Wales was re-elected after receiving 491 first-preference votes - six votes ahead of him.
He told Belfast Live it was not possible to say whether the delayed FOI response had any bearing on the result, but he added: "It simply leaves a bad taste in the mouth about what was going on at the time."
The Electoral Commission confirmed it had received Mr Nicholl's letter.
A spokesperson added: "When we receive a copy of the mentioned report, we will review it and identify if any rules have been broken that fall within our remit.
"The Electoral Commission takes our role as a regulator very seriously. The powers we have to investigate are clearly defined in law and relate to political parties and campaigners in terms of the donations they receive and the money they spend during regulated election periods.
"We do not have investigatory powers relating to electoral fraud and would advise that any allegations of electoral fraud taking place are reported to the police to investigate."
An Information Commissioner's Office spokeswoman said it was considering the council's "compliance" with the FOI Act "in line with the FOI and Transparency regulatory manual".
The council has repeatedly refused to comment on the mayoral expenses controversy.
In a recent FOI response, it told Belfast Live it "forwarded" the internal report to the PSNI and Public Prosecution Service "for further investigation".
The controversy is understood to have become part of a wider PSNI probe into the council which in 2021 saw its Ballymena headquarters raided by detectives.
Ms Wales recently announced she will not be seeking re-election in May, while Ms Donaghy has retired from the council on health grounds.
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