A dispute over a major overhaul of Saskatchewan's labour laws is headed for the Supreme Court of Canada.

The Saskatchewan Federation of Labour said Monday it's asking the country's top court to rule on the constitutionality of the province's essential services law and Trade Union Act.

This comes after the SFL lost the latest round of a five-year court fight with a decision by the Saskatchewan Court of Appeal.

The essential services law puts limits on which public sector workers can go on strike.

The amendments to the Trade Union Act eliminated automatic union certification when more than half the employees in a workplace have signed union cards, potentially making it more difficult to unionize.

The unions want both pieces of legislation — called Bill 5 and Bill 6 when they were introduced in the legislature — thrown out.

The SFL says part of its case rests on whether or not the right to strike is guaranteed in the Constitution as a freedom of association.

It says the essential service law impedes workers' rights to strike and limits unions ability to negotiate.

The Saskatchewan Court of Appeal ruled in favour of the province, saying that the Supreme Court ruled in 1987 that freedom of association does not encompass the right to strike.

However, the appeal court also said the Supreme Court said striking could very well be a fundamental right protected by the freedom of association, according to the SFL.

The labour organization is asking the Supreme Court of Canada for leave to take another look at the case, saying Charter rights are constantly evolving.

Now, it's up to the high court to decide whether or not it wants to do so.