"A candidate, agent, or assistant collecting voting papers on electors' behalf creates an opportunity for someone to interfere with voting documents," she warned.
"It could undermine public confidence in local electoral processes and expose the candidate to allegations of interfering with the vote, regardless of whether the risk is real or perceived."
Bayden Barber said he did not want to comment as he did not know why the question was raised on his behalf by campaign member and political strategist Simon Lusk.
Mr Lusk did not respond to requests for comment.
Other mayoral candidates expressed concern about any widespread collection of papers.
Acting mayor Sandra Hazlehurst said even if the documents were collected in good faith, the secrecy of the ballot had to be protected.
"We just want a robust, honest and transparent election process and we want to protect the candidates."
Acting Deputy Mayor Simon Nixon said he thought there was a "very fine line between interfering with the voting process and being helpful".
"I think you're getting on to shaky ground if you start doing it on scale, you're really starting to interfere with the democratic process."
Waitawhara Tupaea said this would be concerning, while Stuart Perry felt "it kind of smacks of trying to manipulate the vote".
"It's up to [electors] to make their decision whether they vote or not and who they vote for," he said.
Allister Tosh didn't think it was a "huge issue" but worried there would be no monitoring.
Collecting papers is not illegal, but doing so could constitute one element of an offence with certain additional circumstances, Ms Evans said. It was also an offence to possess a voting document, other than the one issued to you, without authority.
And, it was an offence to interfere with someone who is about to vote, or attempt to interfere with a voter when voting.
"This could potentially be breached if a candidate is going door-knocking with the aim of collecting voting documents."
Candidates, or their team collecting voting papers "could place the integrity of the poll in jeopardy, and create legal risks for individual candidates".
"Any allegations of election offences as outlined above will be investigated and reported to the Police."
Voters were advised to post their ballot papers or deliver them by hand to the council offices.