Canada's big city mayors are throwing their support behind Toronto in its fight against the Ontario government's unprecedented use of a constitutional provision to push through legislation slashing the size of the city's council.

The chair of the Big City Mayors' Caucus at the Federation of Canadian Municipalities said Premier Doug Ford's moves have now placed Canadians in a constitutional debate when the limits of how governments can work together within the document have not been tested.

"To see a Canadian province invoke the notwithstanding Clause to change the size of a city council, in the middle of an election campaign, is unprecedented," Iveson said in a statement issued Thursday. "On behalf of FCM's Big City Mayors' Caucus, I am offering full support to the City of Toronto's efforts to protect local democracy."

The comments came as Toronto politicians held an emergency meeting to discuss their next steps a day after Ford's Progressive Conservatives reintroduced the council-cutting legislation with the notwithstanding clause.

Mayor John Tory said the province's actions are "wrong and unacceptable."

"This overriding of the Charter of Rights and Freedoms raises very big questions on a matter such as this one and even bigger questions with regard to profoundly important matters that we may not even know about today that will come up in the future," Tory said.

"We're all here to keep standing up for Toronto and I know we're all prepared to continue to do that because we believe in this city."

Toronto councillors were briefed by the city's legal staff behind closed doors on Thursday morning.

The city had challenged the province's council-cutting legislation in court and a Toronto judge agreed earlier this week that passing the bill in the middle of municipal election campaign violated the freedom of expression rights for voters and candidates.

But Ford quickly announced he'd use the notwithstanding clause to override the ruling, and also said his government would appeal the decision.

The premier said using the clause is necessary to ensure the will of elected politicians trumps the court ruling.

The province's council-cutting legislation would reduce the number of Toronto's wards to 25 from 47, with the city's election set to take place Oct. 22.

The opposition parties have vowed to use procedural tools to delay the bill as much as possible.