BUCHAREST : Calls to boycott a Romanian referendum defining a family as the marriage between a man and a woman trended Wednesday on social media, a day after lawmakers endorsed holding such a vote next month.

Facebook users are using the hashtag #boicot (boycott) to let the authorities know that they will skip the vote likely to be held October 7, which could frustrate efforts to get a turnout of least 30 percent for the referendum to be valid.

Romanian senators voted overwhelmingly on Tuesday evening to change article 48 of the nation's constitution to stipulate that the family is founded on the marriage between "a man and a woman", not between "spouses", as it states now.

Romanian law doesn't allow gay marriages, but critics of this initiative say an explicit interdiction in the constitution will make it almost impossible to change the law in the long run in favour of gay couples.

The government must formally announce the decision to hold a referendum, but as the leader of the ruling Social Democratic Party has publicly supported holding the vote, its approval is viewed as all but certain.

"The referendum will take place on 7 October and will be a crucial moment for the fundamental values of the Romanian society," Social Democratic Party leader Liviu Dragnea wrote on Facebook on Tuesday.

"I supported holding such a referendum and I will certainly go and vote," he added.

The vote in the Senate was triggered by a petition started by a civic initiative called "The Coalition for Family" which managed to gather 3 million signatures in favour of the referendum.

The ACCEPT association, which represents the LGBT community in Romania, accused the Senate of "making homophobia a state value and sacrificing the constitutional protection of many families in Romania."