CAW president Ken Lewenza has written the prime minister about abortion. (CAW)

The CAW has chosen a side in the abortion debate.

The union is making it clear, it is pro-choice.

In an open letter to Prime Minister Stephen Harper, national union president Ken Lewenza outlined the union's stance.

Lewenza wrote the letter in response to Conservative MP Stephen Woodworth’s motion to examine whether the Criminal Code definition of "human being" should be expanded to include fetuses.

"Less than a year into a majority government, we see the debate being cracked open by a member of the Conservative caucus," Lewenza wrote. "Nothing has been as offensive as the suggestion that government may infringe on women’s rights over their own bodies and freedom of choice."

Monday, the CAW will hold pro-choice rallies in Windsor and London, Ont.

CAW local 444 in Windsor will hold its rally at 6:30 p.m. Monday at the intersection of Tecumseh Road East and Turner Road, near the Met Campus of Windsor Regional Hospital parking lot.

The rallies will be staged to counter demonstrations by the anti-abortion group Canadian Centre for Bio-Ethical Reform, which will bring its "new abortion caravan" to London on Monday evening.

The caravans feature graphic photos, poster and large box-body trucks covered in similar photos.

Similar CAW events are planned and have taken place throughout the month of June in cities all across Canada.

"Our choice is pro-choice," states the CAW's national website.

Stephanie Gray doesn't understand why the CAW would wade into the debate over abortion. (Canadian Centre for Bio-Ethical Reform)

"The fear, guilt, and shock tactics behind the caravan works only to alienate the general public," CAW Local 444 second vice president Fran Lasorda said in an email to CBC Windsor. "These tactics are meant to terrify women, rather than work towards a well informed and safe decision."

When contacted by CBC News hours before the rally, Lasorda said she was too busy planning the rally to talk about it.

Local 444 president Dino Chiodo said the rally in Windsor was not planned through his local and had no further comment.

Stephanie Gray, the executive director of the Canadian Centre for Bio-Ethical Reform, called the union's decision to join the debate "mysterious."

"Some conceptions occur in cars. However, until abortions start happening in cars, I don't see why an autoworkers' union would take a position on this matter," Gray said. "Unions should focus on workplace-related matters. Abortion is not a workplace-related matter."

Gray said it's not right for the union to force a universal view on its members. She also her group is not forcing people to view the graphic imagery it will display and distribute Monday.

"We're communicating a message," she said. "Individuals are free to protest and groups which want to exist specifically with a mandate to fight us can do that. But a union exists to address workplace matters."