Montreal ? In a rare public dissent, 19 Catholic priests have denounced the Vatican’s opposition to gay marriage and allowing homosexuals into the priesthood.

In rare public dissent, the clerics signed an open letter that ran Sunday in Montreal’s La Presse newspaper.

The priests said the church was invoking “natural law” to make its case against homosexuality, arguing that slavery was also once considered “natural.”

The letter questions whether the church has “the last word on the mysteries of political, social, family and sexual life.”

“In these matters,” the letter says, “the official teaching of the church has shown itself more than once to be wrong.”

The letter was in response to the position against gay marriage by the Canadian Conference of Catholic Bishops. Recent guidelines of the Vatican’s Congregation for Catholic Education also restated opposition to the ordination of priests with “deep-seated homosexual tendencies.” But the Vatican said there would be no crackdown on gays who are already ordained.

Canada last year legalized same-sex marriage nationwide, a move many clerics of all religions opposed.