Stephen Harper says the practice of covering one's face with a niqab is "rooted in a culture that is anti-women" – his bluntest effort to date to explain why the Conservative government is fighting the use of these veils during Canadian citizenship ceremonies.

The Prime Minister was responding in the House of Commons to Liberal Leader Justin Trudeau, who has sharply criticized the Tories for seeking to ban the covering of women's faces when they are swearing a citizenship oath and has accused Mr. Harper of Islamophobia.

Mr. Trudeau responded outside the Commons Tuesday by declaring that "this government is doubling down on the politics of fear."

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A debate over reasonable accommodation in Canada is playing out again, this time over the niqab. Mr. Harper is arguing, as a Conservative fundraising e-mail recently put it, that is "not the way we do things here," while Mr. Trudeau is championing religious freedom as protected by the Charter of Rights.

Some Muslim women wear face-covering niqabs in public, and the Liberals defend their right to wear the veil during citizenship ceremonies. Mr. Harper, whose government is appealing a Federal Court ruling that would allow people to cover their face while reciting the oath of citizenship, strongly disagrees.

"We do not allow people to cover their faces during citizenship ceremonies. Why would Canadians, contrary to our own values, embrace a practice at that time that is not transparent, that is not open and frankly is rooted in a culture that is anti-women," Mr. Harper told the Commons Tuesday. "That is unacceptable to Canadians, unacceptable to Canadian women."

Alia Hogben, executive director of the Canadian Council of Muslim Women, said Mr. Harper should "do a little bit more thinking" before he speaks on this topic.

She said women are not required under Islam to cover their faces, and none of the women in her organization wear niqabs. But, Ms. Hogben added, "I don't think it's the state's place to tell a woman what to wear or what not to wear."

The council conducted a study of 80 women in Ontario who wear the niqab and found that none of them had any problem with uncovering their face when necessary for security or identification reasons. "It's not that you have to like the niqab, or you're promoting or condoning, but it is up to the women whether she wants to wear it or not," Ms. Hogben said.

Defending his position in the Commons, the Prime Minister suggested Mr. Trudeau is out of step with public opinion, but did not cite polls to back up his statement.

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"The Leader of the Liberal Party continues to bring up his position on the niqab, not seeming to understand why almost all Canadians oppose the wearing of face coverings during citizenship ceremonies," Mr. Harper said.

Mr. Trudeau responded by saying Tuesday's comments prove his allegations that Mr. Harper is using fear of Muslims for political effect.

"This government is willing to confuse and conflate the issues in ways that encourages ignorance about these various elements and quite frankly stokes fears and anxieties at a time where people are worried about terrorism and extremism," he said. "This is the crassest kind of politics."