The Australian Sex Party has threatened Google with legal action after the search engine refused to run its ads on the eve of tomorrow's Melbourne by-election.

It comes after Sex Party ads were blocked by Google at the last federal election because the company - which is typically opposed to censorship - perceived the text as too racy (the ads were reinstated by Google the day before the election).

Fiona Patten, convenor of the Australian Sex Party and candidate for state seat of Melbourne.

Sex Party candidate Fiona Patten said this time the search giant said it would not approve her ads "because we have a donate button on our page and we're not a charity".

"It's giving me the shits that in two elections we've not been able to run ads with Google when all of the other political parties have had no problem," she said.