Although considered one of the most liberal ex-communist nations in the world, Slovenia on Sunday rejected the union of same-sex couples by a large margin in a referendum, according to preliminary results released by authorities.

The results showed that 63.5 percent voted against a bill that defines marriage as a union of two consenting adults, while 36.5 percent were in favour, the Time reported.

Voters also rejected a proposal to allow same-sex couples to adopt children, which was included in the bill.

In March, Slovenia introduced marriage equality, but opponents appealed to the top court to call for a referendum. A civil society group The Children are at Stake also collected 40,000 signatures to challenge the changes before any gay couples could marry, reports said.

Slovenia's conservatives were backed by Pope Francis, who called on the mainly Catholic country to "back the family as a structural reference point for the life of society,'' BBC reported.

"This result presents a victory for our children," said Ales Primc, the group's leader.

"The outcome is a clear defeat of the leftist government, which backed the changes,'' Ljudmila Novak, from New Slovenia, was also quoted as saying.

The latest result demonstrates a cultural split in the EU, where Western member states area granting greater rights to gay people but newer centre and eastern member states area resisting such moves.

The United Left party, which initially proposed the change in the law, meanwhile said the result was a temporary setback.

"It's not over yet. Sooner or later the law will be accepted,'' United Left MP Violeta Tomic said.

Gay rights in the country remain a contentious issue despite the push from EU member states to give equal rights to same-sex couples.

In another referendum in 2012, almost 55 percent of voters in European Union member-states and ex-Yugoslav republics opposed giving more rights to same-sex couples, including the right to adopt the children of their partners, reports said.