Slovakia's leftist prime minister declared on Tuesday that he was ready to back a constitutional amendment defining marriage as a union between man and woman and closing the door to same-sex marriage.
The opposition Christian Democrats and other centre-right parties drafted the amendment that will need support from Prime Minister Robert Fico's Smer social democrats for the two-thirds majority required to change the constitution.
"Smer is willing to support the amendment in exchange for the opposition's support for an amendment introducing changes in the judicial system," Fico told reporters in Bratislava.
"The marriage amendment will not bring about any drastic changes, it only seals in the constitution what is already defined by law," said Fico, whose Smer is a member of the traditionally liberal Party of European Socialists group in the European Parliament.
The European Union's newest member Croatia outlawed same-sex marriage in a referendum last year, triggering a similar constitutional amendment.
Slovak law defines marriage as a "union between a man and a woman".
No form of same-sex civil union is legal in Slovakia, where more than 70 percent of the population of 5.4 million is Christian, according to a 2011 census.
But a 2012 opinion poll showed that 47 percent of Slovaks supported civil unions for same-sex couples while 38 percent were opposed.
Parliament will debate the amendment during a session starting on March 18.
Same-sex marriage is legal in a handful of the 27 other EU states including Britain and France, while civil unions are notably recognised by the Czech Republic, Germany and others.