TORONTO -- A national civil liberties group is joining the fight against a controversial bill by Ontario's cash-strapped government that would force a wage freeze and cuts to benefits on tens of thousands of teachers across the province.

The Canadian Civil Liberties Association echoed teachers' unions in condemning the legislation as unconstitutional and a violation of workers' rights across the province.

They're warning the governing Liberals not to proceed with the legislation that they're pushing through the legislature, or face the consequences in court.

"We understand that budget concerns need to be addressed by government, but budget concerns are no justification to undercut the democratic process," said Sukanya Pillay, a director of the association.

The bill "seriously impairs fundamental rights in a manner that cannot be justified in a free and democratic society," she added.

The legislation, which three unions have vowed to fight all the way to the Supreme Court of Canada, will also give the government the power to ban strikes and lockouts for at least two years.

That's alarming because it removes the right to strike before there's even the threat of one, said Pillay, who plans to seek intervener status in a potential legal challenge of the bill.

Toronto lawyer Steven Barrett, who provided advice on the legislation to the unions, said it doesn't take a constitutional lawyer to conclude that the legislation is an "unprecedented assault" on the rights of educational workers.

The Ontario Liberals are going even further than the federal Conservatives when they forced striking employees at Air Canada and Canada Post back to work.

Unlike the Liberals, the Harper Conservatives didn't give cabinet or a minister the authority to "unilaterally and arbitrarily" impose collective agreement terms, he said. Instead, they left it to independent binding arbitration.

The Liberals, who are facing a $15-billion deficit, have suggested that their bill isn't objectionable because it imposes terms of an agreement it reached with English Catholic and francophone teachers, he said.

"But from a constitutional perspective, a collective agreement exacted by government threats and bullying outside of the lawful rights, protections and procedures of the Labour Relations Act is no more voluntary than a forced confession," Barrett said.

The unions have accused Ontario's self-styled "education premier" of outdoing his Conservative predecessor Mike Harris, whose aggressive agenda to slash spending and cut taxes sparked strikes and even riots at the legislature.

Education Minister Laurel Broten said the government will defend the bill in court and expressed confidence that it will withstand a court challenge.

"We take the position that it is constitutional, that it respects the Charter of Rights and Freedoms, that it respects the right to collective bargaining," she said.

Three unions negotiated an agreement with the province, which the minority Liberals are now trying to impose on three other unions who opposed it. It included three unpaid days off, halving sick days to 10 a year and the elimination of the banking of unused sick days that could be cashed out at retirement.

In 2002, the B.C. government rewrote health-care contracts to allow for widespread contracting out, leading to a 2007 Supreme Court ruling that struck down sections of the law and forced the government to negotiate a $75-million compensation training package.

Broten said her government has tried to avoid the pitfalls that tripped up the B.C. Liberals, namely by showing that they bargained in good faith.

In B.C., the government gave 20 minutes notice to the unions that they were changing the contract. Ontario tried to negotiate for six months with the unions, some of which left the table after an hour and didn't come back, she said.

"The situation here in Ontario is very different from what transpired in British Columbia and I think that Ontarians will know and recognize the difference in the approach that we have taken from what the Harris government would have done or what the Harper government has done."

But experts say negotiating for a certain period of time doesn't guarantee that the legislation will stand up in court. However, Ontario is in a good position to argue that its restrictions on collective bargaining rights are justified because the province has severe financial problems.

The bill will likely become law, as the Progressive Conservatives have agreed to help it pass. Government officials say the final vote could come Sept. 10, about a week after students return to the classroom.