Members of Parliament wearing protective face masks attend the autumn session of the Swiss Parliament with new plexiglas dividers in place and pandemic-related legislation up for debate, amid the COVID-19 outbreak in Bern, Switzerland on Tuesday. Photo: AFP

Switzerland votes Sunday on whether to legalize same-sex marriage after opponents secured a referendum challenging the government's plans to bring in "marriage for all."

Polls indicate broad support for legalization, which would bring the Alpine nation into line with most of Western Europe.

Polling stations remain open until noon, with the result expected to follow within hours.

"Don't miss the opportunity to participate in this historic step towards equality," the Marriage Yes campaign said Saturday, urging voters to the polls.

According to the last survey conducted, 53 percent are in favor of legalising same-sex marriage, with 27 percent against.

Market researchers gfs.bern surveyed 13,261 voters between September 1 and 9.

An earlier gfs.bern survey between August 2 and 16 put the balance of support at 55-20.

The polling showed that members of some Christian congregations and supporters of the right-wing populist Swiss People's Party (SVP) - Switzerland's largest political party - were the most likely to oppose legalizing same-sex marriage. Switzerland decriminalized homosexuality in 1942, but numerous local and regional police forces continued to keep "gay registers," some into the early 1990s.

Same-sex couples can already register a civil partnership, with around 700 such partnerships established each year.

However, this status does not provide the same rights as marriage, including for obtaining citizenship and the joint adoption of children.

After years of debate and discussion, the Swiss parliament approved a bill  in December 2020 allowing same-sex couples to marry in the country of 8.6 million people. But it was challenged under Switzerland's direct democracy system, with opponents gathering the 50,000 signatures needed to put the issue to a referendum.

The government and parliament have urged voters to back "marriage for all," and to eliminate the current "unequal treatment" between heterosexual and gay couples.