The allegation was made in writing to party leader Samantha Ratnam about 8.30am on Thursday.

And it's not the first time scandal has hit the minor party.

"The Greens take allegations of this nature extremely seriously," the party said in a statement.

"At 10.12am Samantha Ratnam personally contacted the complainant to confirm that their message had been received, was being taken seriously and that immediate actions were being taken to initiate an investigation in line with agreed processes."

The woman has asked to remain anonymous and "out of respect for her we don't feel it's appropriate to make any further comment", the party said.

The candidate has been ordered to "withdraw from all campaign-related activities" by the party while investigations continue. It's unclear if this means the man's candidature representing the Greens continues.

He and the electorate he is contesting, have not been named and he will remain on ballot papers.

More than a million people have already voted in the election.

Thursday's scandal is the latest in a string to hit the Greens in recent weeks.

The minor party's first hiccup came with the resignation of upper house candidate Joanna Nilson over a series of embarrassing Facebook posts, including calling federal Liberal MP Michaelia Cash a "disgusting smug parrot" and talk about shoplifting and drugs.

Then it was revealed Footscray candidate Angus McAlpine previously released rap music including misogynistic lyrics detailing date rape.

Party staffer Paul McMillan quit after making social media jokes about Islam, pedophilia and sexist slurs.

Late on Thursday an ABC reporter said Ms Ratnam had withdrawn from a pre-arranged interview scheduled for Friday morning.

Australian Associated Press