As Toronto officials gear up for another legal battle over Ontario's plans to slash the city council, they face a new challenge: Premier Doug Ford's unprecedented use of the controversial "notwithstanding clause" of the Charter of Rights and Freedoms.

So what are their options, amid this unfamiliar legal territory?

"It's going to be an uphill battle," said Nader Hasan, constitutional lawyer and partner at the Toronto firm Stockwoods LLP.

City councillors will meet on Thursday to discuss the province's revised legislation, tabled on Wednesday, which invokes the notwithstanding clause to override a Superior Court judge's ruling that struck down the previous version. The province is looking to reduce the number of council seats to 25 from 47, claiming it will save money.

Never before used in Ontario, or at the federal level, the clause, also known as Section 33, allows governments to pass laws that appear to violate certain charter rights.

It is viewed as a nuclear option and has been politically polarizing — and powerful — since it appeared in the Constitution four decades ago.

"There's very little in the section itself that sets any limits," said Cheryl Milne, executive director of the David Asper Centre for Constitutional Rights, an advocacy group affiliated with the University of Toronto.

Hasan puts it another way: "It is the final say. That's how it was crafted."

But that doesn't mean a challenge is impossible. It's just murky — given the lack of case law because the clause has rarely been invoked successfully — and the result is hard to predict even for scholars of constitutional law.

Premier Doug Ford is invoking the controversial 'notwithstanding clause' of the Charter of Rights and Freedoms to push through the legislation. (Chris Young/Canadian Press)

'Novel' argument possible

Hasan says one possible legal route is to challenge the law by arguing it is an unlawful use of the clause, a claim that relies on the principle that no action in a constitutional democracy like Canada should be entirely immune from judicial review.

There's also a notion posed by some scholars that the clause should only be proactive, not reactive. In other words, it can't be used to go back in time and change a piece of legislation.

"In this case, it is retroactive. The legislation has already been passed, the decision's been made on it," said Joel Bakan, a professor of law at the Allard School of Law at the University of British Columbia.

Another strategy could involve arguing against a key piece of Justice Edward Belobaba's scathing ruling, which deemed the legislation an infringement of the freedom of expression for both candidates and voters; in part because it was introduced partway through the election.

Hasan said a "novel" approach would involve arguing Belobaba was wrong — that the bill actually violated the unwritten constitutional right to effective representation.

Why go that route? Because the notwithstanding clause doesn't apply to an unwritten right, only those specified in the charter.

NDP MPPs banged on their desks and were escorted out one by one at the Ontario legislature Wednesday afternoon as they tried to delay the reintroduction of the notwithstanding clause bill to cut the size of Toronto city council. 2:18

'Very difficult to predict'

Experts also agree that the clause might not be available to use without justification, or certain constraints or criteria being met.

"There are opinions out there that [it's] not just license to go ahead and abandon the charter in any situation," said Bakan.

"But it's very difficult to predict how a court — and ultimately the Supreme Court of Canada — will look at this situation."

Don Eady, a lawyer representing several candidates challenging the province's legislation, is still holding out hope that the city's original plan for a 47-ward system will prevail.

"We're going to continue to fight this until there is nothing left to fight," he said.