The 2 million member Presbyterian Church (USA) will vote on a gay marriage resolution at its biennial convention taking place in Detroit, Michigan.

If approved Friday, Presbyterians would become the biggest Christian group in the United States to allow its congregations to support marriage for gay and lesbian couples, the Detroit Free Press reported.

At its 2012 convention in Pittsburgh, church delegates narrowly (338-308) voted down a similar measure.

Opponents warn that the move would create division between the church and other more conservative Presbyterian churches outside the U.S., while backers argue that the church should lead by example.

Currently, Presbyterian ministers can bless the unions of gay couples so long as ceremonies are not structured as weddings.

In 2010, delegates voted in favor of allowing non-celibate gay clergy, a policy change decades in the making.