Supporters of same-sex civil unions demonstrate at the Piazza delle Cinque Lune in Rome on February 24, 2016. | Filippo Monteforte/AFP/Getty Matteo Renzi wins same-sex union vote Civil partnerships vote was seen as a de facto confidence vote for Renzi.

Italian Prime Minister Matteo Renzi's government won a key vote in the senate Thursday approving its controversial legislation to grant same-sex partners similar rights to heterosexual couples, fending off a threat to his leadership.

The bill was approved by 173 senators, with 71 opposing it and senators from the populist 5-Star Movement — which has 35 seats in the upper house — refusing to take part in the vote. It will now be submitted to the lower house of parliament.

The legislation has disappointed LGBT campaigners, who are angry it was watered down to remove a clause that would have given non-biological parents in a same-sex union parental rights.

That was the price Renzi had to pay for the support of the New Center Right party, which he needed after the 5-Star, Italy's second-largest party, withdrew its support. "Clearly, we're not going to give a confidence vote to Renzi's government," said a spokeswoman for the party in the senate, adding that the bill was a "watered-down version" of the original proposal.

Italy is the only West European country not to recognize same-sex relationships, and Renzi has been promising to deliver civil unions since 2013. Until now, decisions on the status of same-sex couples have been left to local courts.

In 2015 the European Court of Human Rights found Italy must adapt its legislation to meet its obligations under the European Convention on Human Rights to “provide for the core needs relevant to a couple in a stable committed relationship.”

The prime minister tweeted Wednesday that the law was "a historic event for Italy."

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