Prime Minister Justin Trudeau applauded the actions of 25 Liberal MPs from Toronto who signed a letter calling on all members of the provincial legislature to step up and defeat Premier Doug Ford's legislation slashing the size of the city's municipal council.

"Quite frankly, it is something that I expect of all our MPs, to be strong voices for their communities in Ottawa," Trudeau told reporters in Saskatchewan Thursday.

Trudeau said earlier this week that while he is "disappointed" the Ford government decided to use the notwithstanding clause to force the legislation through the provincial legislature, he will not step into the debate over the size of Toronto city council.

"We are calling on all MPPs to defeat Ford's legislation, tabled yesterday at Queen's Park, and the Bill's unprecedented use of the notwithstanding clause in Ontario," said the letter, first obtained by the Toronto Star.

"In particular, we believe MPPs elected in Toronto have a responsibility to defend the city, its democratic institutions, and the rights of citizens to a free and fair municipal election. The people of Toronto deserve nothing less."

Ford announced Monday that he would take the rare step of invoking Section 33 of the Canadian Charter of Rights and Freedoms after an Ontario Superior Court judge ruled that his provincial government's legislation to cut the number of Toronto city councillors was unconstitutional.

Section 33 — known as the notwithstanding clause — allows a government to override for a five-year period rulings on legislation that judges have determined would violate sections of the Charter.

Pierre Trudeau opposed the clause, but reluctantly agreed to its inclusion in order to get a deal on the Constitution Act of 1982, which wrested control of Canada's Constitution from Britain.

NDP Leader Jagmeet Singh said it isn't good enough for Trudeau to praise the actions of his MPs while doing nothing to step in the way of Ford deploying the notwithstanding clause.

"The prime minister is saying, 'I'll defend the Charter,' but not talking about how," Singh said. "I'm saying, listen, let's do the hard work, let's sit down in committee, bring experts to the table and have them discuss what the options are and how they can move forward in a way that brings our nation together."

Politically toxic

Ontario has never used the clause before. Political leaders generally have been reluctant to use the notwithstanding clause, which is viewed by many as politically toxic.

"The correct response to a court decision one disagrees with is to appeal. Ford's response is heavy-handed and disrespectful," the MPs' letter said.

"As elected representatives of the City, we want to assure the people of Toronto that we understand and respect the critical role that city hall and local democracy play in building the communities in which we live."

The letter is signed by all 25 Liberal MPs from Toronto, including several members of the federal cabinet, including: