Canada's Roman Catholic bishops say religious voices have a right to be heard in public debates and shouldn't be shouldered aside in the name of separation of church and state.

They are also encouraging civil disobedience in cases where public policy runs afoul of private morality on questions such as abortion, contraception and gay marriage.

The Canadian Conference of Catholic Bishops has issued a 12-page pastoral letter on religious freedom, arguing that freedom of worship includes the right for believers to publicly state their views on key questions of the day.

The letter says there are radical elements that want to relegate religion to the private sphere, denying it any influence on society.

It says the idea of banning religious feasts and symbols supposedly out of respect for members of other religions or non-believers is a sign of the marginalization of religion, and Christianity in particular.

The bishops also cite abortion, the morning-after pill, gay marriage and euthanasia as areas where the state makes no allowance for conscientious objection.

They say it is wrong for any Roman Catholic to support the right to abortion or euthanasia; rather, there is a clear obligation to oppose them by conscientious objection.

"In a constitutional democracy such as Canada's, the system of justice must strive to protect more effectively freedom of religion and of conscience as key elements of our free and democratic society," the letter said.

The bishops argue that excluding believers from public debate deprives society of an important dimension.

They said they see a disturbing trend of threats to freedom of conscience and religion both at home and abroad.

The right to religious freedom is a litmus test for the respect of all other rights, the bishops said.

"Where it is protected, peaceful co-existence, prosperity and participation in cultural, social and political life flourish," they wrote. "But when it is threatened, all other rights are weakened and society suffers."