ZAGREB (Reuters) - The Croatian parliament ratified on Friday a European treaty that has provoked mass protests by social conservatives who believe it undermines family values in the predominantly Roman Catholic country.

FILE PHOTO: FILE PHOTO: Croats protest against the ratification of the Istanbul Convention in Zagreb, March 24, 2018. REUTERS/Antonio Bronic/File Photo/File Photo

Opponents of the Istanbul Convention say they support its aim of combating domestic violence but reject its definition of gender, which they believe paves the way for introducing transsexual or transgender as separate categories.

In the vote, 110 deputies in the 151-member parliament supported the treaty, drawn up by the Strasbourg-based Council of Europe which promotes human rights and democracy.

To placate opponents, the conservative-led coalition government adopted a separate statement on ratification, saying the treaty will not change Croatia’s legal definition of marriage as a union between man and woman.

“The goal of this convention is to prevent violence against women and within families,” Prime Minister Andrej Plenkovic told the parliament earlier this week. “There is no legal obligation to recognize third sex, change the definition of marriage or our educational program.”

Some lawmakers in Plenkovic’s conservative-led coalition, which has a slim majority with 77 members of parliament, also refused to back the treaty, but opposition deputies helped to ensure its ratification.

The Church and conservative groups joined some members of Plenkovic’s HDZ party in opposing the treaty, which a number of other European Union countries have already ratified.

Last month thousands marched through the capital Zagreb demanding the government to give up on ratification. A similar protest took place in the second biggest city Split on Thursday.

The conservative groups said they would now seek a referendum in the hope of forcing the government to revoke the treaty. To force a vote they need to collect the signatures of 10 percent of all voters, or about 380,000 people.

However, some legal experts say that Croatia’s Constitutional Court might reject the possibility of a referendum on an international treaty which deals with human rights.

Earlier this year two other eastern EU countries, Bulgaria and Slovakia, stopped short of ratifying the treaty due to similar objections about the definition of gender as “social roles, behaviors, activities and characteristics that a particular society considers appropriate for women and men.”