The Official Opposition wants to change labour laws so employees in unionized workplaces are no longer compelled to pay dues even if they don't join the union.
"Ontario is one of the only places in the world where people have to be forced to join a union in order to take employment, and that's wrong," said PC labour critic Monte McNaughton.
"We need to modernize our labour laws and that starts with giving workers a choice, and it's simple: do they want to join a union and pay union dues or not."
McNaughton claimed making Ontario a "right-to-work" province would create tens of thousands of jobs.
Labour Minister Yasir Naqvi called the Tory plan an unconstitutional "job-killer," and quoted U.S. President Barack Obama in describing it as "the right to work for less."
"If you look at the evidence on what the right-to-work-for-less has done across the United States, wages and benefits go down for all workers, unionized and non-unionized," said Naqvi. "We have evidence that shows that health and safety laws are weakened, and also there is a net loss of jobs."
The New Democrats warned the proposal from PC Leader Tim Hudak would not help create jobs or boost the economy.
"The Conservatives are on a mission to crush organized labour in Ontario, and I think that is a big mistake," said NDP Leader Andrea Horwath. "The drive to push down wages and to get rid of the labour movement is not the path to prosperity."
The Ontario Federation of Labour made "Challenging Hudak's Anti-Worker Agenda" the theme of its annual convention in Toronto this week.
"Hudak's Tories hope that by attacking workers they can drive a wedge between unions and the public, but voters have no interest in the politics of division," OFL president Sid Ryan said in a statement.
"Attacking workers' rights backfired on (former premier Dalton) McGuinty, and it will be the downfall of Hudak."
Naqvi said the Tories were far more interested in union bashing than in giving workers choice on union dues.
"It is attacking unions, and a way to take away the constitutional right to bargain collectively," he said.
The NDP said the Progressive Conservative proposal would end up putting even more pressure on the already shrinking middle class in Ontario.
"If these plans ever were to come to pass, Mr. Hudak would just squeeze more people out of the middle class, drive down wages and make life worse for thousands and thousands more Ontarians," said Horwath.
"The fact that he has such little vision that he would take those ideas and bring them here is nothing short of shameful, and will not help Ontario one iota."
McNaughton insisted the Tory caucus was united on the "right-to-work" bill, but the initiative was approved by only 53 per cent of party delegates at a policy conference in September.