"He said he was offering a cash incentive of $50 if I agreed to vote for National in this year's election.
"I have called the appropriate number to report this incident but thought I would make others aware," Copeland wrote on the Beach Haven and Birkdale Community page.
She told the Herald the man was wearing blue jeans, a light-blue shirt and a big blue badge that said vote National.
"It was so strange I didn't even know what to think," said Copeland, a 31-year-old Labour voter.
"I said, 'No thank-you, I have already voted and it's not for National' and I just closed the door."
Four people on her street later told her they had received the same offer from the man.
"I didn't think for a second he was working for National. I think he might have been on a one-man crusade. There was nothing professional about him."
She had told the commission, giving a description of the man and called the police.
The police told the Herald they were looking into its enquiries but were uncertain if they could reply today.
The National Party's Northcote candidate, MP Jonathan Coleman said his electorate office had been told of the alleged bribe.
"That is absolutely nothing to do with the National Party."
"I don't know who it is. It could be anyone. It could be a mentally ill or drunk person. It's certainly nothing that we would contemplate doing. It's a corrupt practice.
"The National Party do not have badges that say 'vote National'."
A number of people made comments on Facebook about Copeland's post.
"Sounds like an obsessed random on a mission," one said of the man alleged to have offered the bribe.
"I can't imagine any party would do that," another said.
A commission spokeswoman said it was an offence to give money to a voter to induce them to vote or refrain from voting.
"The offence of bribery is set out in section 216 of the Electoral Act 1993. It is a corrupt practice offence and carries a maximum penalty of up to two years imprisonment and/or a fine up to $100,000 for a candidate, party or registered promoter, or $40,000 in any other case."