OTTAWA -- The Roman Catholic archbishop of Toronto is asking Justin Trudeau to reconsider his decision to bar would-be Liberal candidates who do not endorse the party policy on abortion.

Cardinal Thomas Collins wrote to the Liberal leader Wednesday to say he is deeply concerned about the controversy.

Collins said he understands the need for party discipline, but questions whether that discipline can extend to matters of conscience.

"Political leaders surely have the right to insist on party unity and discipline in political matters which are within the legitimate scope of their authority," Collins wrote.

"But that political authority is not limitless: it does not extend to matters of conscience and religious faith. It does not govern all aspects of life."

Trudeau has said the party won't accept new candidates who are unwilling to vote pro-choice on relevant Liberal legislation, although sitting MPs will be allowed to run even if they oppose the practice.

The party issued a statement late Wednesday that acknowledged Collins's perspective while gently declaring it would not be moved.

"Like all other Canadians, Cardinal Collins has the freedom to express his deeply held beliefs," said Trudeau spokeswoman Kate Purchase.

"We obviously respect the cardinal, and his views. This is a matter of rights, and Canadians need to know that when they vote Liberal they will get representative who supports and defends women's rights."

In his letter, the cardinal reminded Trudeau -- who was raised in the Catholic faith of his famous father -- that the patron saint of politicians, Thomas More, was executed for following his conscience against the political authority of his day.

Collins pointedly mentioned that there are two million Catholics in his diocese. He said he encourages them to get involved in politics as both voters and candidates.

"It is not right that they be excluded by any party for being faithful to their conscience."