OTTAWA - Conservative MPs are under intense pressure from the Prime Minister's Office (PMO) to vote against a Tory MP's non-binding motion that calls on Parliament to study when human life begins.

Tory sources say Prime Minister Stephen Harper wants southern Ontario MP Stephen Woodworth's motion eliminated before Parliament rises for the summer in late June.

"The PM himself wants this vote beaten down," one source tells QMI Agency.

The PMO is said to be telling MPs that voting in favour of Woodworth's motion would be like forcing Harper to break his promise not to "reopen the debate on abortion."

Tories who side with Harper are said to be putting the screws to their colleagues by telling them that a vote in favour of Motion 312 is a vote against Harper's leadership.

However, the Institute of Marriage and Family Canada is trying to counter that pressure.

"When all that is at stake is a discussion, then I believe to say no to the discussion is to say we will not have free speech on this issue," said spokeswoman Andrea Mrozek.

Meantime, the group 4MY Canada has an online postcard campaign promising support to Tory MPs who favour Woodworth's motion when they face nomination contests before the next federal election.

The motion calls for a Parliamentary committee to consult scientists, ethicists and others about the validity of the 400-year-old definition of human being that states someone becomes human only at the moment of full birth.

MPs debate the motion on Thursday and vote on it next Wednesday.