The Electoral Commission is referring a Progressive Party advertisement to the police.
The commission says the advertisement, relating to the drug BZP, which appeared in a Southland paper in April, breached the Electoral Finance Act.
It says the advertisement did not publish a promoter statement from the party, which is led by Cabinet Minister, Jim Anderton.
In a separate matter, the Commission is to also refer an anonymous phone call from someone purporting to be push-polling, to the police.
It says that would need a promoter statement, and it will be sending an advisory note to parties about the issue.