“What we don’t need and what I just can’t support is change being rammed down our throats without a single second of public consultation and on top of that done in the middle of the election period itself,” said Mayor John Tory, who discovered the plans from a news report on Thursday night and is calling for a referendum on the matter.

“You don’t change the rules in the middle of the game,” he said. “That is not right and that is not fair.”

Toronto is the biggest metropolis in Canada and the fourth largest in North America, with 2.7 million residents and cranes jutting up all over its downtown core to build condominiums for many more.

The City Council is renowned for unwieldy and circular debates, and offers the mayor only one vote — which greatly frustrated both Mr. Ford and his brother, who were unable to gather the votes for many of their promises, particularly a subway expansion into the east of the city.

So the announcement to reduce the 47 seats to 25 took on a distinctive personal flavor, with Mr. Ford punishing his former opponents at Toronto’s City Hall, particularly given that the proposed changes affect no other cities in the large province.

While the premier and Toronto’s mayor are both political conservatives, they were adversaries for the mayoralty in 2014, when Mr. Ford stepped into his brother’s place on the ballot after Rob Ford was found to have a rare form of cancer that proved terminal. Mr. Tory won the election handily.

“I was down at city hall for four years,” Mr. Ford said at the news conference. “I was there when we’d take 10 hours to made a decision. It is the most dysfunctional political arena in the country.”