Private litigant Graham McCready has filed court documents alleging Prime Minister John Key assaulted an Auckland waitress when he repeatedly pulled her ponytail.
Mr Key has apologised to Amanda Bailey for pulling her hair over several months whenever he visited Rosie Cafe near his Parnell home.
He gave two bottles of his own-label wine to the waitress and has said his actions amounted to horseplay.
But Mr McCready described it as the intentional application of force to the woman's person, which was not consented to, in court documents filed today.
Mr McCready, whose legal work led to an initially successful prosecution of former Auckland Mayor John Banks, filed the paperwork at the Auckland District Court this morning.
He told reporters it was a serious issue.
"What Mr Key is trying to say, of course, is 'this is a trivial, one-off thing, I made a mistake'," Mr McCready said.
"The consequences of this type of stuff are not trivial, they can be long-lasting."
Mr McCready said Ms Bailey, her employer and Mr Key's wife, Bronagh Key, made it clear he should stop but he continued.
He had not heard from Ms Bailey, despite trying to contact her, he said.
Meanwhile, a Unite Union spokesperson said the union was representing Ms Bailey.
Ms Bailey had sought its support and it would be advising her on employment issues, as well as helping to resolve concerns about how her identity was revealed by a newspaper.