With the US Supreme Court about to release its decision on same-sex marriage, more than 50,000 Catholic, Orthodox, Protestant, and Jewish leaders have signed a pledge affirming their position that marriage is between a man and a woman and vowing to draw the line.

"There are clear, distinctive doctrines and differences between us," said conservative activist Deacon Keith Fournier of the Diocese of Richmond, who is one of the co-drafters of the pledge, according to the Catholic News Agency.

The pledge warned the US Supreme Court that it "has no authority to redefine marriage."

"The institutions of civil government should defend marriage and not seek to undermine it. Redefining the very institution of marriage is improper and outside the authority of the State," according to the pledge.

It said marriage is "ontologically between one man and one woman, ordered toward the union of the spouses, open to children and formative of family."

The pledge said marriage as one between a man and a woman was not an idea manufactured by the Christian Church.

"Though affirmed, fulfilled, and elevated by Christian teaching, the truth that marriage can exist only between one man and one woman is not based on religion or revelation alone, but on the Natural Moral Law, written on the human heart and discernible through the exercise of reason," it said.

The Christian leaders vowed to defend marriage as what it is, saying that if the Supreme Court allows same-sex marriage, "the precedent established will leave no room for any limitation on what can constitute such a redefined notion of marriage."

They said allowing same-sex marriage will send a message that children do not need a mother and a father, adding that this will undermine fundamental rights and threatens security, stability and future.

"As Christian citizens united together, we will not stand by while the destruction of the institution of marriage unfolds in this nation we love," they said.

When same-sex marriage will be allowed, according to the pledge, the government will enforce it using the police power of the state.

"This will bring about an inevitable collision with religious freedom and conscience rights. We cannot and will not allow this to occur on our watch," according to the statement.

It said the Supreme Court will undermine its legitimacy if it redefines marriage and it will decrease its credibility and impair its role as a moral authority.

"It will be acting beyond its proper constitutional role and contrary to the Natural Moral Law which transcends religions, culture, and time," it said.

The signatories vowed that "as Christians united together in defence of marriage, we pray that this will not happen. But, make no mistake about our resolve. While there are many things we can endure, redefining marriage is so fundamental to the natural order and the true common good that this is the line we must draw and one we cannot and will not cross."

The Southern Baptist Convention (SBC) has also come out strongly against same-sex marriage.

About 5,000 delegates, LifeSite News reported, passed a marriage resolution last Wednesday against same-sex marriage.

"God in His divine wisdom created marriage as the covenanted, conjugal union of one man and one woman," the statement said.

It added, "Southern Baptists recognise that no governing institution has the authority to negate or usurp God's definition of marriage. No matter how the Supreme Court rules, the Southern Baptist Convention reaffirms its unwavering commitment to [natural] marriage."