On the eve of a vote on a private member's motion that calls on Parliament to study the details of precisely when a baby can be considered a human being, the NDP is slamming the one high-profile member of cabinet who has indicated he plans to support it.

In a press conference Tuesday morning, NDP critic for the status of women Niki Ashton noted that Prime Minister Stephen Harper has repeatedly stated his opposition to reopening the debate.

In that light, Ashton told reporters in Ottawa the official Opposition is, "extremely concerned by the fact that a senior government member, a cabinet minister Jason Kenney, has come out in support of this motion."

The motion is being championed by Conservative backbencher Stephen Woodworth, who argues it is not intended to revive an abortion debate.

Instead, he has repeatedly emphasized his position that, if passed, it would only create a committee to study the legal definition of when a child becomes human.

Specifically, it proposes the establishment of a 12-member, all-party committee to focus on section 223 of Canada’s Criminal Code. Under the existing law, a child is considered a human being once he or she has completely emerged from the womb.

Critics have long charged, if passed, Motion 312 could lead to a change of that definition and as a result might represent a first step toward banning abortion.

The prime minister has deflected those allegations with his unwavering insistence the government has no interest in going down that path.

Answering reporters' questions Tuesday, Ashton said the facts appear to belie that position. And in "thousands" of phone calls and emails fielded by the NDP, she said Canadians have indicated they agree.

"What irks so many Canadians," Ashton said, "is the fact that they believed Stephen Harper, but what they're seeing ... doesn't reflect what they heard from the prime minister."

Suggesting that the ruling Conservatives have used private member's bills to propel their party's agenda in the past, Ashton suggested Woodworth's motion should never have gotten this far.

Ashton said the fact it has, indicates the ruling Conservatives aren't as averse to the debate as they've suggested.

"Here we have a senior cabinet minister ... we know that is close to the prime minister, who has clearly said that he will be supporting this motion. If that doesn't challenge the statement that this government isn't willing to reopen the debate I don't know what does."

The prime minister has made it clear members of his caucus will be free to vote their conscience when it is put to the House Wednesday night.

Kenney, a devout Roman Catholic, said Monday he would be voting in favour of the controversial motion.

"I think we can have a respectful debate on this question and, like I said, the big tradition of all parties in government is to allow a free vote on questions of conscience,” Kenney said at a press conference.

The federal Liberals and the Green Party have both come out in opposition to the motion. Woodworth has said he nevertheless believes members from all parties will vote in favour of his motion when it is put to the final vote.