BUCHAREST (Reuters) - Romania moved a step closer to ruling out the possibility of legalizing same-sex marriage on Wednesday when its top court paved the way for a referendum on defining marriage in the constitution as a union strictly between a man and a woman.

Members of Romania's gay community attend the Gay Fest 2014 pride parade in Bucharest June 7, 2014. REUTERS/Bogdan Cristel

The nine judges on the Constitutional Court ruled unanimously that a proposal signed by 3 million Romanians this year to change the constitution’s definition of marriage was valid.

Under Romanian law, the constitution can be changed after a proposal by the president, the government, a quarter of the members of parliament or at least 500,000 citizens. Parliament must approve the revision, which must then pass a nationwide referendum.

Few politicians openly support same sex marriage in the socially conservative eastern European nation of 20 million, where the Orthodox Church holds considerable sway.

Currently, the constitution says family starts “on the basis of freely consenting marriage between spouses”.

The Coalition for the Family, a civic initiative, gathered 3 million signatures earlier this year in favor of replacing “spouses” with “a man and a woman”. It said only men and women can naturally start a family and raise children.

Local LGBT rights groups say the revision would, if approved, effectively make it impossible to legalize same sex marriage at a later date.

Chief Justice Valer Dorneanu said the court did not rule on the substance of the proposal but on whether it met legal requirements.

“It is not in the Constitutional Court’s attribution to decide whether it will admit (same-sex) marriage in our constitution, nor to redefine the notion of family,” Dorneanu was quoted as saying by state news agency Agerpres.

“The court had to rule strictly on whether the revision proposal was constitutional.”

Twenty-eight human rights groups, including Amnesty International, had previously urged the court to reject the proposal.

“The Constitutional Court’s decision ... regarding the citizen initiative that aims to ... narrow the definition of family and implicitly ban any possibility to legalize same sex marriage is regrettable,” LGBT rights groups MozaiQ and TRANSform said in a joint statement.

“The initiative creates a hostile, degrading and derogatory environment for the LGBT community in Romania.”

Another local LGBT rights group, ACCEPT, urged parliament to ensure the referendum question clarifies the distinction between family and marriage.

“The political class must not forget that family is an inclusive institution based on love and respect that includes homosexual couples, single-parent families or unmarried heterosexual couples,” it said in a statement.

The referendum could occur at the same time as a parliamentary election later this year. Parliament is currently in its summer recess.