Switzerland will hold a referendum on whether to push ahead with same-sex marriage.
MPs adopted a bill recognising same-sex marriage in December, several years after many other Western European countries.
But opponents of the law have gathered the necessary signatures to call for a referendum, the authorities said on Tuesday.
Switzerland's largest party, the populist SVP, had warned that they would launch a referendum bid against December's law.
In Switzerland, most laws and other acts passed by parliament come into force without the people being asked to vote.
But a referendum is possible when citizens who oppose certain decisions collect 50,000 valid signatures within 100 days of the official publication of the act.
According to the Swiss Federal Chancellery, the request for a referendum on same-sex marriage gathered more than 61,000 valid signatures.
The SVP has stated that it is "intolerable to want to place marriage on an equal footing with any form of cohabitation".
The date of the vote has not yet been set, as Swiss citizens are used to voting three or four times a year on a variety of issues under their system of direct democracy.
Switzerland adopted its bill on same-sex marriage in 2020 after a long parliamentary battle and fierce support from the Green Liberals party.
Previously, same-sex couples could enter into "registered partnerships" that did not give them the same rights as marriage.
But the new legislation allowed them to wed and have access to sperm donation, while transgender citizens could also change their legal gender with a declaration.
However, the legislation did not include provisions for allowing same-sex couples to have children.
A survey commissioned by Pink Cross in 2020 showed more than 80% of Swiss support same-sex marriage, suggesting the law would take effect even despite the referendum.
"It's really about time after more than 20 years that Switzerland finally takes this step," said Roman Heggli, Managing Director of Pink Cross.
Heggli told Euronews that a rejection of same-sex marriage would be "a huge catastrophe" for the country.
"It's a really big step in the acceptance of gay people in general .. it would make a huge difference."
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