ROME — Tens of thousands of people opposed to gay rights rallied Saturday in Rome’s Circus Maximus against legislation that would permit civil unions for same-sex couples and grant them legal recognition as families.

Massimo Gandolfini, organizer of Saturday’s “Family Day” protest, told the crowd that the legislation now in the Senate needs to be defeated.

“A man and a woman form a marriage,” Gandolfini said. “The others are alchemy.”

The coalition government of Premier Matteo Renzi is pushing for the legislation granting civil unions, including the right of inheritance, to receive the pension of a deceased partner, or to make medical decisions about a partner in hospital. But the provision to permit homosexuals to adopt the biological children of their partner is the most hotly contested, even within the coalition.

Cabinet ministers expressed dissent during the rally.

Interior Minister Angelino Alfano sent his support to the protesters via a Twitter message. Environment Minister Gian Luca Galletti attended the protest, saying he supported the civil unions but not the so-called “step-child adoption” clause.

“I think this is a big step backward simply because it doesn’t defend the rights of the weakest,” he told Sky. “Children need to have a mother and a father.”

The Rome rally comes one week after tens of thousands of people rallied in nearly 100 cities across Italy in favour of the law. The crowd in the Circus Maximus, among them robed Catholic friars as well as politicians from across the spectrum, waved placards reading: “No to civil unions.”

There was dispute about the number of people joining the protest Saturday. Gandolfini announced that two million people attended, but opposition groups put the numbers at closer to 300,000.