TORONTO -- As Ontario's legislature prepared to hold a rare midnight sitting to debate a bill that would cut the size of Toronto city council, members of Canada's legal community called on the government not to overrule a court decision striking down an earlier version of the legislation.

On Sunday afternoon, an open letter signed by about 400 Ontario legal professionals was sent to Attorney General Caroline Mulroney asking that she not support the use of the Constitution's notwithstanding clause.

The clause was invoked by Bill 31, dubbed the Efficient Local Government Act, which reintroduces legislation that was struck down by an Ontario Superior Court judge.

The judge ruled that the initial bill violated the charter rights of candidates and voters in Toronto's upcoming election.

The new bill, which slashes the number of Toronto councillors to 25 from 47, was debated at an uncommon weekend sitting at Queen's Park on Saturday.

The lieutenant-governor granted the government's request to reconvene the house at 12:01 a.m. Monday to continue to expedite passage of the bill.

Will Hutcheson, a family lawyer based in Toronto and author of the letter, says the provincial government's use of the clause violates the rights of both the candidates in the election and the citizens of Toronto.

"I think it's really dangerous to use the notwithstanding clause," said Hutcheson. "Rights can be overwritten by the notwithstanding clause ... that means the charter really doesn't protect our rights the way Canadians have thought it does."

Hutcheson said he wrote the letter on Wednesday and published it online, and since then it has been signed hundreds of times. He said he is sending it to Mulroney and her office on Sunday ahead of the midnight sitting.

"We, the undersigned members of the legal community, are writing this open letter to you because your office is assigned to champion and safeguard the fundamental principles of the rule of law and due process in Ontario, and the rights of the people," reads the letter. "We are gravely concerned about Premier Doug Ford's proposed use of the notwithstanding clause."

A second letter, sent to Ford and Mulroney and signed by more than 80 law professors from across the country, calls the Ontario government's use of the notwithstanding clause "a dangerous precedent that strikes at the heart of our constitutional democracy."

The professors say they recognize that it is within the government's power to invoke the notwithstanding clause, "but it should never be the first resort -- it should be the last."

"The notwithstanding clause must be the exception -- not the rule," states the letter spearheaded by University of Toronto professor Brenda Cossman.

The letter notes Ford has suggested he would not hesitate to use the clause in the future and says his invoking it in this instance is "challenging the core principles underlying our constitutional democracy."

The professors say it rejects the role of an independent judiciary in upholding the fundamental rights and freedoms of every person in Ontario.

The Ministry of the Attorney General did not immediately respond to a request for comment on Sunday.

Earlier this week, City of Toronto clerk Ulli Watkiss said that with each passing day it becomes "virtually impossible" to ensure the city provides its residents and candidates with a fair election.

Government House Leader Todd Smith has said that the city needs certainty around its election, which is set for Oct. 22, so the bill must be passed quickly.

Opposition Leader Andrea Horwath said New Democrats would continue to oppose the use of the notwithstanding clause, saying Ford has dragged the entire province into a "personal grudge match against Toronto."

"The best chance of allowing Toronto to hold a fair, democratic election this fall is for Bill 31 to be withdrawn," Horwath said in a release Sunday evening.

The government finds itself crunched for time at the legislature with the International Plowing Match in Chatham-Kent set for Tuesday and each year Queen's Park closes for a day so all politicians can attend.

The midnight sitting will allow the Tory government to reach the needed 6 1/2 hours on this stage of debate to push the bill forward in the legislative process.