Thousands of people opposed to gay rights are gathering in Rome's Circus Maximus to protest against legislation that would permit marriage-style unions for same-sex couples and grant them legal recognition as families.

Massimo Gandolfini, organizer of Saturday's "Family Day" protest, told Sky Tg24: "Italy is one of the few western countries that is still resisting this deviation."

Premier Matteo Renzi's coalition government intends to legalize same-sex civil unions and permit homosexuals to adopt the biological children of their partners. But some Cabinet ministers are expressing dissent.

Interior Minister Angelino Alfano sent his support to the protesters via a Twitter message. Environment Minister Gian Luca Galletti attended the protest.

Galletti told Sky: "My values are not negotiable."

The crowd, among them robed Catholic friars, waved placards reading: "No to civil unions."