"By a single stroke, every law where rights depend on marital status -- such as employment discrimination, employment benefits, adoption, education, health care, elder care, housing, property and taxation -- will change so that same-sex sexual relationships must be treated as if they were marriage," it said.
"That requirement, in turn, will apply to religious people and groups in the ordinary course of their many private or public occupations and ministries -- including running schools, hospitals, nursing homes and other housing facilities, providing adoption and counseling services, and many others."
Four Catholic bishops were among the 39 religious leaders signing the letter: Cardinal-designate Timothy M. Dolan, archbishop of New York and president of the U.S. Conference of Catholic Bishops; Bishop Salvatore J. Cordileone of Oakland, Calif., chairman of the USCCB Subcommittee for the Promotion and Defense of Marriage; Bishop William E. Lori of Bridgeport, Conn., chairman of the USCCB Ad Hoc Committee for Religious Liberty; and Bishop Kevin C. Rhoades of Fort Wayne-South Bend, Ind., chairman of the USCCB Committee on Laity, Marriage, Family Life and Youth.
Other signers included top representatives of the Southern Baptist Convention, the Lutheran Church-Missouri Synod, Church of Jesus Christ of Latter-day Saints, Assemblies of God, the Church of the Nazarene and the Salvation Army, along with a collection of smaller Protestant denominations, seven pan-Christian associations including the National Association of Evangelicals, and two representatives of Orthodox and Hasidic Judaism.
Religious employers would "face lawsuits for taking any adverse employment action -- no matter how modest -- against an employee for the public act of obtaining a civil 'marriage' with a member of the same sex. This is not idle speculation, as these sorts of situations have already come to pass," the letter said. "Even where religious people and groups succeed in avoiding civil liability in cases like these, they would face other government sanctions -- the targeted withdrawal of government cooperation, grants or other benefits."
The letter cited the case of Portland, Maine, which required Catholic Charities to extend spousal employee benefits to same-sex domestic partners as a condition of receiving city housing and community development funds.
"There is no doubt that the many people and groups whose moral and religious convictions forbid same-sex sexual conduct will resist the compulsion of the law, and church-state conflicts will result," the letter said.
Because those who object to giving equality to same-sex partners have been marked as "bigots, subjecting them to the full arsenal of government punishments and pressures reserved for racists," the letter predicted other consequences if same-sex marriage were to gain more legitimacy.
"These punishments will only grow more frequent and more severe if civil 'marriage' is redefined in additional jurisdictions," it said. "Because law and government not only coerce and incentivize but also teach, these sanctions would lend greater moral legitimacy to private efforts to punish those who defend marriage."
The push to alter the definition of marriage "warrants special attention within our faith communities and throughout society as a whole," the letter said, because such an action would have "grave consequences," including interfering with the "religious freedom of those who continue to affirm" traditional marriage.
"The promotion and protection of marriage -- the union of one man and one woman as husband and wife -- is a matter of the common good and serves the well-being of the couple, of children, of civil society and all people," the letter said.
The value of traditional marriage transcends any society or government, is "a universal good" and is the "foundational institution of all societies," it said.