Maryland's leading Catholic bishops say they oppose gay marriage because it erodes religious freedom.

In a document titled The Most Sacred of All Property: Religious Freedom and the People of Maryland that is being distributed among churches and state policymakers, the bishops argue that “efforts to alter society's long-standing definition of marriage … infringe upon the religious liberties of individuals and institutions that acknowledge heterosexual marriage not only as a fact of nature but also as an article of faith.”

Ignoring that gay couples can marry in 10 countries, 6 states and the District of Columbia, the bishops claim that marriage between one man and one woman has “remained constant” in recent decades.

“It is based not on a social prejudice, but rather on the recognition that the union of a man and woman is the only possible source – and their married relationship the best possible environment – for the children who will become society's next generation.”

According to the Maryland Catholic Conference, the document is being sent to Maryland's nearly 280 Catholic parishes. Leading elected officials will also receive a copy of the 16-page document, which was signed by Washington Archbishop Donald Cardinal Wuerl, Baltimore Apostolic Administrator Archbishop Edwin F. O'Brien and Wilmington Bishop W. Francis Malooly.

Last year's effort to legalize marriage in Maryland for gay couples ran aground after religious groups lobbied heavily against its passage.

Governor Martin O'Malley has pledged to shepherd the bill through this year's legislative session, which opens in January.