The Supreme Court of Canada ruled in favour of workers Thursday in a pay equity case involving women at Canada Post that was originally filed 28 years ago.

The Public Service Alliance of Canada (PSAC) claimed in August 1983 that women were being discriminated against under the Canadian Human Rights Act because they made less than men in comparable Canada Post jobs.

After lengthy proceedings, the Canadian Human Rights Tribunal ruled  in the workers' favour in 2005. 

PSAC had originally asked for $300 million, but the tribunal reduced the damages by 50 per cent to $150 million.

In 2008, the Federal Court overturned that decision in a ruling that was subsequently upheld 2-1 by the Federal Court of Appeal, with Justice John Evans dissenting.

'We respect the decision of the Supreme Court of Canada and will abide by their ruling.'

—Canada Post

But the Supreme Court last year agreed to hear a final appeal and on Thursday, in a rare decision delivered orally after the parties had made arguments, ruled unanimously in favour of the workers.

"We agree with the dissenting reasons of Justice Evans in the Court of Appeal, which comprehensively address the issues on these appeals. We would allow these appeals with costs," Chief Justice Beverley McLachlin said in delivering the top court's brief decision.

PSAC national executive vice-president Patty Ducharme said Thursday that she didn't expect the ruling to come so soon.

"They were back in 20 minutes, and they reinstated the tribunal's original order, and we're thrilled," Ducharme said on Power & Politics with Evan Solomon.

Ducharme said the ruling applies to a group of office workers for Canada Post.

"There are men that work in that classification level as well," she said. "Originally there were 2,300, and there's probably about 6,000 that have come in and out of that classification. But they will indeed see a chunk of cash."

Ducharme couldn't say exactly when the money would be distributed, but she told Solomon the workers could have the money within a year.

"We'll be pushing to ensure that people get the money as soon as humanly possible," she said.

Ducharme told CBC News that with interest, the decision could mean up to $250 million in damages for clerical staff who worked at Canada Post between 1983 and 2002. That figure is an estimate and the precise damages figure after interest is not yet clear. 

Canada Post says it will 'abide' by ruling

"We respect the decision of the Supreme Court of Canada and will abide by their ruling," Canada Post said in a statement Thursday.

The case centred on whether the human rights tribunal acted correctly in comparing the female employees' wages to the male-dominated group that nevertheless included some high-paid women.

The Federal Court had held that such a comparison was "irrational" and "patently unreasonable."

In the late 1990s, the federal government settled a pay equity dispute with 230,000 current and retired employees to the tune of $3.2 billion.

The Conservatives sought to bring an end to the lengthy and costly court battles over pay equity when they passed a controversial measure in 2009 requiring workers to secure pay equity during collective bargaining rather than in courts and tribunals.

With files from The Canadian Press