The Australian Sports Party should apologise for a Facebook photo featuring a topless woman jogging, a women's rights group says.

The picture is accompanied by an anecdote about the woman, described as "voluptuous" and a "babe", who is running with a sign around her neck saying, "If you catch me, you can have me".

Wayne Dropulich of the Australian Sports Party was elected to the Senate in last September's federal election, before the WA count was declared void due to missing ballots.

The party is fielding candidates, including Mr Dropulich, in the re-run of the WA Senate election on April 5.

Early voting is underway with 50 polling centres opened in Perth and in regional areas.

Fair Agenda director Rebecca Wilson says the Sports Party's Facebook campaign material is a troubling sign.

"It's just not cricket for parties aiming to represent us in the Senate having these kind of attitudes towards women," Ms Wilson said.

"No-one wants to see naked women in their Facebook feed when they're looking to learn about politics."

The Facebook post describes a man successfully losing weight by chasing two women wearing the signs, one of whom is described as a "voluptuous, athletic 19-year-old babe dressed in nothing but a pair of running shoes".

Wayne Dropulich and the Australian Sports Party are under fire over a Facebook post featuring a topless woman ( 7.30 )

It also describes how the man loses a dramatic amount of weight when he is ultimately pursued by a "huge muscular guy ... wearing nothing but pink running shoes and a sign around his neck that reads, 'If I catch you, you are mine'."

The ABC has approached Mr Dropulich for comment.

Fair Agenda has started an online petition calling on the party to remove the post and issue an apology.

Ms Wilson says the Sports Party has dropped the ball.

"I thought it was a bit silly and gross and just a bit backwards to be honest," she said.

"I was really shocked that a candidate running for our federal Senate would post something like that. It just seems inappropriate that someone vying for our votes could treat women in that way."