WATCH: Gay Priest Speaks Against Minnesota Marriage Amendment

Father Bob Pierson, a gay priest in Minnesota, told a group of 200 Catholics last month that they can vote against the amendment that would place a same-sex marriage ban in the state constitution this November.

Pierson, who belongs to a monastic community at St. John's University in Collegeville, gave the advice in a speech June 10 at an event in Edina, according to MinnPost. The speech has received more than 30,000 views on YouTube, where Minnesotans United for All Families, the coalition working to defeat the ballot measure, posted it.

"I believe this amendment violates an important principle in Catholic teaching and that as Catholics, we can vote no," Pierson said.

Pierson said his argument was based on the principle of freedom of conscience. He referred to the writings of "a young theologian by the name of Joseph Ratzinger," now known to the world as Pope Benedict XVI, for support.

"Over the pope as expression of the binding claim of ecclesiastical authority, there stands one's own conscience which must be obeyed before all else, even if necessary against the requirement of ecclesiastical authority," wrote the future leader of the Roman Catholic Church in 1967.

The comments put Pierson at odds with the Catholic hierarchy in Minnesota, where Archbishop John Nienstedt of St. Paul and Minneapolis has told priests he would tolerate "no open dissention" on the marriage ban. Several dioceses have spent more than $1 million to promote the ballot measure, according to MinnPost.

A Public Policy Polling survey from June showed support for the measure declining, with 49% of voters opposed compared to 43% in favor. Most of the shift has come from independent voters, who now oppose the ban by 54% to 37%.