Slovakia will hold a referendum in February on whether to maintain a ban on same-sex marriage in the largely Roman Catholic EU member, President Andrej Kiska said on Thursday.
Slovakia's parliament amended the constitution in June to define marriage as a union between man and woman, effectively closing the door to same-sex marriage and stirring protest among rights groups.
The conservative Alliance For Family nevertheless went ahead with gathering the 400,000 signatures needed in the country of 5.4 million people to call the referendum, now scheduled for February 7, 2015.
The vote will also focus on adoption rights for same-sex couples and on whether sex education and lessons on euthanasia should be made compulsory at school.
Gay rights activists in the country, where seven in 10 people identified themselves as Christian in a 2011 census, slammed the referendum as setting a dangerous precedent.
"The fact that the majority will vote on the rights of a minority opens up a Pandora's box," gay rights activist Romana Schlesinger told AFP.
Slovakia's ombudswoman Jana Dubovcova said "turnout will show whether these issues are as important to voters as they are to the organisers of the referendum".
Only one of the seven referenda held in Slovakia since 1993 was valid -- one on EU entry -- as turnout in the rest failed to reach the required 50-percent threshold.
No form of same-sex civil union is legal in Slovakia, but a 2012 opinion poll showed that 47 percent of Slovaks supported civil unions for same-sex couples while 38 percent were opposed.