More than 60 groups have filed briefs against same-sex marriage to the US Supreme Court, with most of the opposition coming from religious organisations and some Republican officials.

By comparison, more than 370 businesses and groups including employers such as Google have filed "friend-of-the-court" briefs in support of gay marriage. Many prominent Republicans have also filed briefs in support.

The hearing is scheduled for 28 April, to be followed by a ruling on the hotly-contested issue.

The US Conference of Catholic Bishops along with evangelical, Mormon, Baptist, Lutheran, Methodist and other religious organisations have warned that legalising same-sex marriage will lead to serious future conflicts between Church and State.

The Billy Graham Evangelistic Association is among those organisations that have warned of threats to freedom of speech among traditional believers, and that people of faith face being marginalised if they continue to hold to their view that marriage is between a man and a woman.

Religion News Service listed 16 states led by Republican governors as among those calling for bans to be upheld, including Michigan, Ohio, Kentucky and Tennessee. In nine of these states, Alabama, Alaska, Arizona, Idaho, Kansas, Montana, Oklahoma, Utah and West Virginia, bans on same-sex marriage have already been struck out by federal courts.

A further 18 states have submitted briefs to the Supreme Court opposing bans on same-sex marriage.

The case will result in a national ruling, compared to 2013, when the Supreme Court decreed that it was up to federal governments to grant benefits to married same-sex couples.