Ontario employers can no longer force their employees to quit working at age 65.

An amendment to the Ontario Human Rights Code goes into effect Tuesday to prevent seniors from facing age discrimination at work, and it makes mandatory retirement illegal in the province.

Mandatory retirement was already banned in several provinces and territories, including Alberta, Manitoba, Quebec, Prince Edward Island, Nunavut, the Yukon and the Northwest Territories.

Labour Minister Steve Peters said Ontario residents should also be able to choose when to retire based on their lifestyles, circumstances and priorities.

Jim Bradley, the Ontario minister responsible for seniors, said older workers have valuable experience to share, and deserve to be evaluated based on their performance rather than on assumptions about people their age.

The province estimates about 4,000 of the 100,000 Ontario residents turning 65 each year will take advantage of the new law.

But at least two union leaders weren't cheering the change.

Wayne Samuelson, president of the Ontario Federation of Labour, said he worries the government is preparing to increase the age at which people can access government pensions, since that is what happened in the United States and the United Kingdom after those countries abolished mandatory retirement at 65.

"So what's really going on here is they're paving the way for people to work longer, mainly because of the fact we're all living longer," Samuelson told the Canadian Press.

Buzz Hargrove, head of the Canadian Autoworkers Union said it's not just those over 65 who could be hurt by the change. Hargrove said those who count on worker turnover to open positions for them will find it harder to land a job.

"It does undermine our policies in how we generate opportunities for young people," he said.

He added that most of the people who would benefit from the amendment are white-collar workers who could likely find work after age 65 even without the change.

The Ontario legislature passed the amendment in December 2005, but gave employers a one-year transition period that ended Dec. 12, 2006.

According to the Ontario government, there are 1.5 million seniors in the province, and the province will have 3.7 million residents over the age of 65 by 2031.

With files from the Canadian Press