However, an expert in bad behaviour in the workplace said these polices were becoming more common, particularly in the wake of the Harvey Weinstein scandal.

The ministerial sex ban was announced on Thursday by the Prime Minister, who moved to limit the damage from the Barnaby Joyce scandal.

It was earlier revealed that Mr Joyce had separated from his wife, with whom he has four daughters, and is in a relationship with his former media advisor Vikki Campion, who is pregnant with Mr Joyce's child.

The affair has raised serious issues about the culture of sex and power inside Parliament House and deficiencies in the ministerial code of conduct, Mr Turnbull said when he imposed the ban.

On Friday, the Prime Minister said while most people would have regarded the ban as "not needing to be said", he wanted to spell it out.

"Certainly from now, ministers must not have sexual relations with their staff."

University of Canberra School of Law and Justice assistant professor Bruce Baer Arnold has slammed the decision, labelling the Prime Minister a "nanny".

"I think it's fairly fundamental in Australia that consenting adults are free to do what they want to do as long as there is no harm to anyone else," assistant professor Arnold said.

'If we're concerned about the rights, the freedoms and the dignity of all Australians, adults should be free to do what adults want to do."

He said when prohibitions like the "bonking ban" were imposed, greater problems arose.

"It deprives adults of their dignity and there are real questions as to whether it is enforceable. I'm sure people, staffers and otherwise, will continue to do what they've done in the past, but possibly they will be a bit quieter about it.

"Telling people who they can and cannot sleep with could have worked for Menzies perhaps, but it won't work now. People should be treated as adults, their privacy should be respected and we shouldn't treat them as somewhat naughty children."

He said the hurt caused to Barnaby Joyce's family was "tragic", but laws should stay out of the bedroom.

Assistant professor Arnold said the attention given to the ban following Mr Joyce's affair was "largely a diversion".

"What we should be concerned about is ... an abuse of power rather than the relationship as such," he said.

SACS Consulting managing director Andrew Marty, an expert on addressing bad behaviour in the workplace, said it's becoming more common for workplaces to implement policies like this.

"What is common sense to one person, another person will be completely unaware of," he said.

"Policies are being implemented far more now, particularly policies about the appropriateness of relationships. Historically we didn't see that, we left it up to people's judgement to do the right thing."

Mr Marty said the Weinstein scandal, where the movie mogul was accused of sexual assault by more than 50 women, had shed a new light on issues of power imbalances in the workforce.

"In general it's regarded as very poor form for workplaces to tolerate sexual relationships where there is a power difference," he said.

"Parliament is catching up with plenty of organisations where it is considered to be extremely unacceptable for a senior person to have a sexual relationship with a less senior person.

"You can't, strictly speaking, ban it in these environments, but it is certainly regarded as inappropriate behaviour or bad governance."

Sex Discrimination commissioner Kate Jenkins said leaders needed to take action to set the appropriate tone for a workplace.

She said the change to ministerial code of conduct had started an important conversation about consensual relationships.

"In this case, the Prime Minister has decided that it's necessary to change the code of conduct. I don't think a blanket ban is necessary in all cases, there is not a one size fits all solution because not all workplaces are the same."