OTTAWA – The notwithstanding clause is once again on the tongues of political figures in Canada, as it has been periodically since it came to be three decades ago. But what is it really?

With Ontario Premier Doug Ford saying he will be using the notwithstanding clause to force cuts to Toronto’s city council despite a scathing court ruling that said it violated the Charter, and amid Alberta’s suggestion that it’s an option for Prime Minister Justin Trudeau to revive the currently stalled Trans Mountain pipeline expansion, here’s an explainer on the often-controversial clause.

The clause, otherwise referenced as Section 33 of the Canadian Charter of Rights and Freedoms, allows the federal parliament or provincial legislatures to pass legislation that overrides certain Charter-established rights and freedoms, for five-year periods.

“It allows a government to pass a law that does something that the courts have said violates rights and is not justified,” said University of Ottawa associate law professor Michael Pal on CTV News Channel.

If a parliament or legislature is successful in invoking Section 33, the legislation they pass to override the Charter has a maximum five-year time limit. Upon its expiry, the government would have to either re-enact the legislation, or it would no longer stand.

“The notwithstanding clause is a very serious matter,” said University of Ottawa vice dean and associate professor of law Carissima Mathen on CTV’s Power Play

“I think that there is a place for the notwithstanding clause. Some people don’t agree, I think there is a place for it, but it requires a certain gravity and a certain sense of seriousness,” she said.

What can be overwritten?

The sections of the Charter that can be overwritten by the implementation of the notwithstanding clause are Section 2, regarding fundamental freedoms such as expression, conscience, association, and assembly; and Sections 7 to 15 regarding the right to life, liberty, and security. The clause cannot be used on a number of other sections of the Charter, including those concerning democratic rights, mobility, and language rights.

How did it come to be?

It was first added to the constitutional accord in 1981 under then-prime minister Pierre Trudeau, despite his stated opposition, following a conference with the First Ministers and in part thanks to a compromise by then-justice minister Jean Chretien. It came into force as an amendment to the Constitution in 1982.

According to a Library of Parliament paper last revised in 2018, opinion has been largely divided on the mechanism since its creation, with many prominent legal figures raising concerns with how the clause would be used.

When has it been used?

As Toronto Mayor John Tory stated on Monday, the clause was put in the Charter for “very extraordinary circumstances.”

Ford’s intention to invoke the clause will mark the first time ever for an Ontario government.

To date it has been used in Quebec on issues of language, and invoked to varying levels in Saskatchewan, Alberta, and the Yukon.

The federal government has never invoked the notwithstanding clause.

With files from CTV News' Ryan Flanagan, and The Canadian Press