Bill Donohue, president of the New York-based Catholic League, has called on Catholics to support an amendment to the U.S. Constitution which would define marriage as a heterosexual union.

Donohue cited President Barack Obama's evolution on marriage equality in calling for passage of the amendment.

In 2004, Obama said that he was opposed to such unions. Four years later, he reiterated his opposition, saying that as a Christian “God's in the mix.”

“God got thrown from the mix in 2012,” Donohue wrote, a reference to Obama's endorsement in May of that year.

Last week, Obama said that he believes the U.S. Constitution guarantees a right to marry for gay couples.

“I think the Equal Protection Clause does guarantee same-sex marriage in all fifty states,” he said.

Donohue said that in making the statement, Obama had “teed up a confrontation between our long-established constitutional right to religious liberty and this newly invented right to gay marriage.”

“The time is ripe for Catholics to support … the federal Marriage Protection Amendment,” Donohue said.

“As any astute political science undergraduate knows, there is no constitutional right to gay marriage,” Donohue asserted. “But now that this issue has been thrust upon us by our constitutional law professor president, we need to affirm marriage between a man and a woman in the U.S. Constitution.”

A majority of American Catholics, however, support gay rights. According to a Pew Research Center report published earlier this month, 57 percent of self-identified Catholics support marriage equality and 70 percent said that society should accept homosexuality. Support among adult Catholics under 29 was even stronger, with 75 percent in favor of marriage equality and only 13 percent saying homosexuality should be discouraged.