Independent candidate Yvonne Weldon took to social media on Saturday to share an account of what she alleged was one of Ms Moore's volunteers taking her corflutes away in Redfern and replacing them with signage in support of Australia's longest-serving lord mayor.
Ms Moore, who is fighting to retain the keys to Sydney Town Hall after 20 years in the role, apologised over the incident.
"I'm sorry this occurred. This absolutely should not have happened," Ms Moore said in a statement.
"I'm told the volunteer was instructed to rectify and replace immediately."
Clover Moore says a rival candidate's signage was replaced after being removed by a volunteer. (Steven Markham/AAP PHOTOS)
Ms Weldon said the incident was disappointing, unacceptable and "emblematic of why we need change."
"After 20 years, the time is right for fresh leadership," she said.
"My team is running for a better kind of politics.When they go low, we go high."
Ms Moore is among the 37 mayors up for election and political analyst Ben Raue cautioned against putting too much stock in recent reports she might not retain her job.
The 78-year-old's team had a history of winning slim majorities and again faces fractured opposition, he said.
"If you look at Clover's vote, it's tended to bounce up and down," the founder of the Tally Room election website told AAP.
"It's hard to see who would be the one to beat her."
More than four million people will cast ballots across 128 councils with several facing an unavoidable shift to the left, after the Liberals' headline-grabbing debacle in which 140-odd endorsed candidates were not nominated.
Local Government Minister Ron Hoenig urged residents to get up to speed with candidates so they could make an informed decision with councils spending more than $22 billion a year on services and infrastructure.
"We need to elect councillors who are competent and hard-working so make your vote today count," Mr Hoenig said.
The elections have been marked by a lack of Liberal candidates after many weren't nominated. (Bianca De Marchi/AAP PHOTOS)
Elsewhere, 140,000 voters in Sydney's fast-growing southwest had the chance to weigh in on the well-publicised fight between Liverpool's Liberal mayor and the Labor state government.
Labor had attempted to address alleged serious maladministration and dysfunction in the council and defer elections, only to run out of time due to the mayor's legal challenges.
The absence of the Liberals will also likely result in Penrith, Camden, Northern Beaches and Blue Mountains councils shifting left, though the Liberals could win seats in Parramatta.
The first council poll since the national housing crisis took hold was also test as to whether affordable dwelling policies could succeed at the local level.
Voters across NSW have been casting their ballots in local government elections. (Steven Markham/AAP PHOTOS)
More than 50 candidates - including Ms Moore - have taken a pledge with pro-development group Sydney YIMBY, which has won support from Liberal Senator Andrew Bragg and senior state Labor ministers.
David Borger, who chairs a pro-development alliance that includes Sydney YIMBY, said it was outrageous so many were lining up to block new homes "in the middle of the worst housing crisis we've ever seen".
"We need to ensure Sydney councils make place for everyone, not just for those who already own property and want to keep others out," he told AAP.
Not every area is being forced to the ballot box, with rural residents in Cowra, Junee and Berrigan enjoying an election-free Saturday after the number of nominations matched or fell short of available seats.
