OTTAWA -- Manitoba's attorney general led a call on the Harper government Monday to amend its new prostitution bill and remove a section that makes it illegal for sex workers to communicate for the purposes of selling their services.

Attorney General Andrew Swan said the Manitoba government supports Bill C-36, the Conservative bill that creates new offences for clients and pimps but does not generally criminalize prostitutes themselves.

But Swan said he has serious concerns about one section of the bill that still makes both parties guilty if they communicate to purchase sex in a public place, or in a place where people under 18 are present.

That section should be removed to make the legislation much more impervious to a court challenge, he said.

"If the bill is amended as we're suggesting, it makes the risk of a successful challenge just far less likely," Swan said in an interview prior to his testimony before a Commons committee.

Earlier Monday, Justice Minister Peter MacKay testified that even though the bill is constitutionally sound, he fully expects it will be challenged again at the Supreme Court of Canada.

MacKay refused to say what parts of the bill are most vulnerable to a Charter challenge as he opened a marathon round of hearings by the House of Commons justice committee -- a rarity in the summer months when the Commons is in recess.

But Swan said the bill "would force those engaged in street prostitution to ply their trade in more isolated and dangerous locations, would put their safety at risk and certainly could jeopardize constitutionality of the legislation."

The Supreme Court struck down Canada's old prostitution law last year, finding it violated the basic Charter right to security of the person and unduly increased the physical risk to prostitutes.

The court imposed a December deadline on the government to replace it with a new law that would comply with the Charter of Rights and Freedoms.

MacKay said the bill is sound law and is highly "defensible."

He said it balances the need to protect communities from prostitution -- including children -- while protecting the prostitutes themselves, whom he says the government considers victims.

The vast majority of witnesses who testified Monday over six hours of hearings agreed the section that still criminalizes sex workers should be amended or removed, said Liberal MP Sean Casey, a member of the committee.

The only exceptions were MacKay and his department officials, Casey said.

Swan said he applauds Ottawa for adopting the "Nordic model" of Sweden, Norway and Iceland, which criminalizes clients and third parties, but not prostitutes. It also includes social programs aimed at helping sex workers.

But the sections in need of amendment "are completely inconsistent with the Nordic model in terms of punishing and re-victimizing the victims of sexual exploitation."

MacKay has said he is open to amending the bill, but he has dropped strong hints that will have limits.

"As sure as night follows day, there will be challenges when new bills are presented," MacKay told the committee. "So we believe that the likelihood that it will be challenged is very real."

NDP justice critic Francoise Boivin said she wants the government to send the bill back to the Supreme Court for another opinion on its constitutionality, but MacKay ruled that out.

The Supreme Court, combined with his department's internal legal advice, has already provided the government the guidance it needed, he said.

There is widespread disagreement among women about how the government should regulate prostitution.

"This bill does nothing to protect the rights of sex workers in this country," said Jean McDonald, executive director of Maggie's: The Toronto Sex Workers Action Project.

"We will see more murdered and missing women as a result of this legislation."

Alice Lee, of a group called Asian Women's Coalition Ending Prostitution, said Asian women are over-represented in the Canadian sex industry, including massage parlours. Many don't know their rights and fear being arrested for breaking the law, she said.

Lee's group supports the bill because it criminalizes "the purchaser and the men that are doing the harm."

Diane Matte, a community organizer from Montreal, called on opposition parties to support the legislation.

Matte's group recently surveyed 109 women working as prostitutes, and found about 80 per cent of respondents wanted out of the profession, but didn't know how to proceed, she said.

"I think it's important to hear that cry, and it's important to stop looking at prostitution as something that is happening between two consenting adults."

Prostitution itself was actually legal in Canada under the old law, but most related activities -- including communicating in a public place for the purposes of prostitution, pimping and running a brothel -- were criminal offences.

The new bill also cracks down on advertising and selling sexual services in public places where a child could reasonably be expected to be present.

By Thursday, the committee expects to hear from more than 60 witnesses, including sex workers, indigenous women and community workers.