Security was tight as pro-gay marriage protesters filled the streets of Zagreb ahead of a referendum which would define marriage as a union between a man and a woman in the Croatian constitution.
The ruling centre-left coalition urged citizens to reject the referendum, supported by the conservative opposition in the largely Catholic country.
They say it would be a major setback to the country which joined the EU in July, a sentiment echoed by the protesters.
“I am here to vote against,” said one man at the demo. “I call on everyone else to do the same. These matters have no place in the constitution because there should be possibilities for society to progress and not to get obstructed – particularly in times of economic crisis when we should be discussing labour rights.”
The referendum was called after the Catholic group “In the Name of the Family” gathered over 750,000 signatures in support of a vote.
Family law already defines marriage as a heterosexual union, but a change to the constitution would be more binding.
Earlier this year, the government hinted that it would have allowed same-sex couples to register as life partners – giving them similar rights to those already enjoyed by heterosexual couples.