Police have been called in to investigate suspected postal vote tampering in council elections.
The Victorian Electoral Commission detected a "pattern of irregularities" in votes from two wards in two separate councils in outer Melbourne, with multiple postal ballot packs appearing to be from the same voter.
Commissioner Sven Bluemmel said he could not speculate on what happened or who was behind it but signalled it "indicates nefarious intent rather than being accidental".
He said there were 128 "suspicious returns" for Whittlesea Council's Lalor Ward and 61 for Knox City Council's Baird Ward, prompting the commission to refer the results to the Victorian Civil and Administrative Tribunal and Victoria Police.
Some 85 votes appear to be fraudulent and checks against the remaining 104 votes were inconclusive, with more than 22,000 votes counted across the two wards.
He said it "appeared election interference had occurred".
"I cannot say precisely how many fraudulent completed votes would have progressed to counting, however it is clear that the results of the elections could have been impacted," Mr Bluemmel told reporters on Wednesday.
There was an unusual number of requests for replacement ballots, he said, but as the vote is secret the commission doesn't know of whom they were cast in favour.
Mr Bluemmel said it "appears to be similar (to what) may have happened" in the northwest ward of Moreland City Council's 2020 election, now known as Merri-bek City Council.
In June, former councillor Milad El-Halabi was fined $20,000 and handed an 18-month community work order after admitting to one charge of vote tampering.
El-Halabi was found to have "possessed and handled" 23 fraudulent ballot papers, which elected him to Moreland's northwest ward, before approving their return to the state's electoral commission, Judge Stewart Bayles said at the time.
Vote integrity has come under the spotlight in recent polls, with the Australian Electoral Commission launching an integrity assurance task force in 2017 and the issue flaring during US presidential elections.
In 2021, Scott Morrison's federal government proposed a voter ID and requirement of people to show identification before voting in federal elections and referendums, however it was withdrawn.
Alleged postal vote tampering in Victoria affected fewer than one per cent of all votes but it can erode public trust, University of Melbourne political science lecturer Heath Pickering said.
"It is not clear why the original ballot pack is not excluded by the Victorian Electoral Commission from the count," Dr Pickering said.
"All ballot packs have barcodes to identify them.
"If a second ballot is sent because the original did not arrive, then the original should be flagged immediately if the commission receives it."
Mr Bluemmel said he was required by law to complete vote counting and all declared councillors would retain their position "until such time as anything else changes".
Election interference carries a maximum penalty of five years in prison and a $99,000 fine per offence in Victoria.
Local Government Minister Melissa Horne described it as a serious matter.
"Any instance of voter fraud is unacceptable, erodes community trust and diminishes the institutions where it has taken place," Ms Horne said.
She commended the electoral commission for rapidly identifying the matter.
