Lawyer Peter Gall, who represented Canada Post five years ago at the Supreme Court of Canada as part of a seemingly endless pay equity battle, says there's a reason why it's so difficult to resolve these issues.

Paying women equally for the same job — everyone accepts that, he said. Where it becomes complicated is in the methodology and statistical analysis of determining whether someone is underpaid relative to someone else for jobs of equal value.

"Certainly to a layman like myself, not trained in statistics, it just seems like gobbledygook," he said, adding one needs to have a PhD in statistics to be able to interpret and analyze the data.

"You have this battery of experts that are speaking a language that nobody understands. How you measure jobs in terms of whether they are of equal value — how you determine whether there is some sort of inequity —is enormously enormously complex."

The case he worked on began with a complaint in 1983 that female clerical workers in the post office were being paid less than their male counterparts in other post office jobs. The case meandered along until 1993 when the Canadian Human Rights Tribunal began hearing evidence.

Yet it wasn't until 2005 that it came to a decision, awarding $150 million to thousands of female postal workers. Six years later, following union losses in the lower and appeals court, the Supreme Court weighed in, upholding the tribunal's ruling.

This poster from the Canadian Union of Postal Workers makes the case that rural carriers, who are mostly female, are being paid less than their suburban counterparts. (CUPW)

Now Canada Post is facing a different pay equity issue, this one involving rural letter carriers. It has been one of the main stumbling blocks in the collective bargaining process between management and the Canadian Union of Postal Workers.

Although a tentative deal was reached this week, it's still unclear how much progress was made on the issue of whether rural letter carriers, who are mainly female, should be getting paid as much as their urban counterparts.

But Canada Post is just one of many employers that have faced this issue — one that can take years to wind its way through courts and tribunals before any kind of settlement is reached. In 2006, Bell Canada employees agreed to a $100 million pay equity settlement, a case that had begun in 1992. In 2012, female nurses working in the federal public service won a $150-million human rights settlement following an initial complaint in 2004.

It's no wonder that management will wage long, drawn-out battles over these cases, given a loss can cost a company millions of dollars.

"The fact that a hearing in this matter would take years to complete shows how complex and controversial this is," Gall said.

'Systemic gender discrimination'

But the reason this continues to crop up in the workplace is rather straightforward, said Mary Cornish, a labour law specialist and chair of the Ontario Equal Pay Coalition.

"There's systemic gender discrimination in the labour market which produces unequal compensation incomes for men and women on a whole variety of different ways. So you keep getting it."

An open letter sent to Justin Trudeau on Tuesday, signed by 200 women including actress Sarah Polley, author Naomi Klein and social activists Maude Barlow and Judy Rebick, called on the prime minister to keep his promise to support equal pay for work of equal value.

"We are asking you to use your influence to ensure that rural and suburban mail carriers achieve pay equity with (urban) letter carriers."

But Gall, while not commenting on the recent Canada Post case, said there is no area of law or policy more complex than trying to measure jobs to determine if they deserve equal pay.

'Hire a battery of experts'

"You couldn't go into a business and say 'OK, let's just do this in half an hour.' You can't. You'd have to hire a battery of experts and there would be disagreements galore."

It's not that employers don't want to pay men and women fairly, said Sophie Fleming, a compensation consultant who deals with pay equity issues. But evaluating jobs can be a tedious process, she said.

"I do think there is a gender gap, obviously, there is one. I don't think it's the intention on the part of the employers that they, generally speaking, will want to pay female jobs lower than male jobs," Fleming said. "But the process of rectifying that is onerous."