A tweet by Labour leader David Cunliffe on Saturday, the day of the Christchurch East by-election, has been referred to police.
Cunliffe published a message on his Twitter profile urging Christchurch East residents to vote for Labour candidate Poto Williams.
"If you are resident in Christchurch East don't forget to vote today - for Labour and Poto Williams!" he wrote.
Under Electoral Commission rules, no campaigning of any kind is allowed on election day.
The Electoral Commission announced this afternoon it had referred Cunliffe to the police saying it believed he had breached the Electoral Act.
It said Cunliffe had allegedly breached the act because the message "was a statement published on polling day advising, or intended, or likely to influence electors as to the candidate for whom they should or should not vote in the by-election".
Cunliffe said this afternoon the party had been advised of the escalation by the Electoral Commission.
"I understand this is a routine part of the Commission’s process.
"I will be co-operating fully with any inquiry and won’t be making any further statement on this matter as it is now part of a formal process."
"I take responsibility for that, the tweet was sent in error and deleted within seconds and it was reported as soon as possible to the returning officer," he said.
He was not aware of the rules at the time.
If found guilty Cunliffe faces a fine of up to $20,000.
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