The man who initiated the private prosecution of John Banks has turned his sights on Labour Party leader David Cunliffe.
Graham McCready, a retired Lower Hutt accountant, has previously taken a successful private prosecution against Labour MP Trevor Mallard.
Mr Cunliffe is being investigated over a tweet sent on the day of the Christchurch East by-election last Saturday urging support for Labour candidate Poto Williams
The Electoral Commission believes that's a breach of the Electoral Act because it was published on polling day. It has referred the matter to the police.
Mr McCready says he wants to give notice that if police won't prosecute Mr Cunliffe, then he will.
However, a law professor says it is unclear whether tweeting encouraging people to vote for a candidate is illegal under the electoral law.
Professor Andrew Geddes of Otago University's law school says tweeting is not specifically covered under electoral law.
He says with tweeting, people have to want to follow the tweeter, and whether that counts as unlawfully distributing material urging people to vote for a candidate is not yet known.