The Vatican is alarmed at what it sees as the erosion of religious freedom in the United States, warning of a threat of “unprecedented gravity” to the Catholic Church’s “liberty and public moral witness.”

Vatican Secretary of State Tarcisio Bertone conveyed a message from Pope Benedict XVI in a letter to the Knights of Columbus’s annual convention in Anaheim, Calif., suggesting a concerted effort is being made to “redefine and restrict the exercise of the right to religious freedom.”

The Pope has long been an admirer of the First Amendment and the balance that the American system has struck between church and state until recently, hence his particular concern.

The letter warns that a brand of secularism is taking hold in America that seeks to exclude the Catholic Church from participating in the debate about issues affecting the future of the nation.

It concludes urging the Knight of Columbus and other Catholic laity to counter the spread of militant secularism in American culture.