Hollande is expected to introduce legislation legalizing same-sex marriages at a Cabinet meeting Tuesday, but parliamentary debate initially thought to be a formality has been put off until January amid rising opposition.
Cardinal Andre Vingt-Trois, head of the French Council of Bishops, labeled gay marriage "the ultimate deceit" during a sermon Sunday, France 24 reported Monday.
The Catholic cleric's opposition joins similar reservations from Protestant, Muslim and conservative Jewish leaders who have announced their opposition.
Members of Hollande's Socialist party hit back against the church. A National Assembly member and the author of the same-sex marriage bill, Erwann Binet, said the church had "strayed from its role" as a religious institution by becoming part of public secular affairs.
He called on the church to "open its eyes to the realities of the families that constitute the modern society -- single parent families, families headed by same-sex couples, families where couples are remarried."
The bill also faces opposition from rural government leaders. About 1,200 mayors have asked for a "conscience clause" to be inserted, giving them the option to not offer marriage licenses to same-sex couples if they don't want to.
The request highlights divergent attitudes in France toward homosexuality, France 24 said. In cities, gays and lesbians are widely accepted, but in the rural countryside attitudes are far more skeptical.