"The freedom of churches must be protected," the Swiss Evangelical Alliance has said after same-sex marriage received overwhelming public support in a referendum.
Nearly two thirds of Swiss (64.1%) backed the 'Marriage for All' proposal in the nationwide referendum.
Gay couples have already been able to enter into civil partnerships since 2007.
Although the proposals have now passed the referendum, it could be several months before the change comes into effect.
Commenting on the result, the Swiss Evangelical Alliance said 'Marriage for All' went "too far" and "places too little weight on the rights of children".
"The wishes of adults have triumphed over the rights of children," it said.
It voiced further concerns about the development of further legislation in the future to permit egg donation and surrogacy.
"An extremely dubious instrumentalization of the human body was not given enough consideration," it said.
The Swiss EA has vowed to stand up for the religious freedom of pastors and churches following the vote.
It said churches must be free to wed only heterosexual couples.
"The Swiss Evangelical Alliance will continue to campaign for freedom of religion and freedom of conscience with regard to church weddings," it said.