Dignity USA has held previous Masses in the chapel of the Roman Catholic-sponsored school, said Detroit chapter President Glenn Crane.
The group was aware that protests were expected Sunday, said Dignity USA Executive Director Marianne Duddy-Burke. She said the group simply hopes to be able to pray in safety.
"Our faith is very important to us," Duddy-Burke said. "Most Catholics would be appalled to know that fellow Catholics cannot easily access our sacraments, have a Mass. We also believe we are all children of a loving God and should be able to worship in peace."
American Family Association Michigan President Gary Glenn said he has asked Archbishop Allen Vigneron to enforce Vatican policies on homosexuality and intervene.
"By allowing the use of its campus chapel by a homosexual activist group that is harshly critical of Catholic doctrine regarding marriage and homosexual behavior, Detroit's Marygrove College is violating a Vatican directive expressly banning the use of facilities at Catholic colleges by such groups," the association said in an e-mail.
In his letter to Vigneron, Glenn said gay sex and those who defend it stand outside the Catholic belief system.
"As is well-known, the Catechism defines homosexual behavior as 'acts of grave depravity ... intrinsically disordered ... contrary to the natural law. ... Under no circumstances can they be approved,'" Glenn wrote. He asked the archbishop to consider Vatican teachings on the "inappropriateness of allowing such an organization to use Church buildings, especially for religious services."
The 1.3 million-member archdiocese declined direct comment on the Dignity USA event, saying only that church institutions are subject to Catholic beliefs.
"There are hundreds of Masses celebrated in the Detroit archdiocese every weekend," archdiocese spokesman Ned McGrath said. "It's always Archbishop Vigneron's expectation that these liturgies are conducted in full conformity with the Catholic Church's teachings and practices."