Forty-seven prominent conservatives have signed an open letter warning the mainstream media against using data on hate groups compiled by the Southern Poverty Law Center (SPLC).

The letter calls the SPLC a "discredited, left-wing political activist organization that seeks to silence its political opponents with a 'hate group' label of its own invention."

Founded in 1971, the SPLC gained fame by successfully prosecuting legal cases against white supremacist organizations, including the Ku Klux Klan. It describes its mission as "fighting hate and bigotry and ... seeking justice for the most vulnerable members of our society."

Today, the SPLC is best known for tracking hate groups, which the organization defines as having "beliefs or practices that attack or malign an entire class of people, typically for their immutable characteristic." Currently, the SPLC says 917 hate groups are operating in the United States.

SPLC's "hate map" gained prominence in the media after last month's deadly violence at a white nationalist rally in Charlottesville, Va. However, critics say the organization has falsely slapped the "hate group" label on non-violent groups who hold traditional beliefs about hot-button issues such as gay marriage and abortion.

Last month, a prominent evangelical ministry based in Florida filed a federal lawsuit accusing the SPLC of defamation after it was labeled an "active hate group." In July, Fox News found that at least seven organizations are listed as hate groups by the SPLC despite explicitly prohibiting violence by their members.

The letter also warns that receiving the SPLC's hate group label "endangers the lives of those targeted with it." It references the 2012 shooting at the headquarters of the Family Research Council in Washington. The gunman, Floyd Lee Corkins, said he disagreed with the group's opposition to gay marriage and prosecutors said he selected the group as a target using the SPLC "hate map."

"By recklessly linking the Charlottesville melee to the mainstream groups named on the SPLC website," the letter went on, "we are left to wonder if another Floyd Lee Corkins will soon be incited to violence by this incendiary information.

Prominent signatories of the letter include Brent Bozell of the Media Research Center, Tony Perkins of the Family Research Council and former Attorney General Edwin Meese III.