Meeting in Baltimore, the SCLC board took a unanimous vote of "no confidence" in Justice Thomas, the court's only black member.
The group said in a strongly worded resolution that it was "profoundly disturbed" by his decisions since he joined the court five months ago after a bruising confirmation battle.
"Justice Clarence Thomas has failed to demonstrate the compassion, sensitivity, independence and intellectual courage . . . that was the prayer of the SCLC," the group said.
The resolution said the SCLC had hoped Justice Thomas would be "a compassionate and independent, although conservative voice."
Instead, the group said, Justice Thomas has shown a "harsh conservatism," sided consistently with Justice Antonin Scalia, the court's most conservative member, and joined what it called the court's "tilt in favor of the rich and powerful."
The vote, taken at a closed session of the SCLC board, brought the group into line with the National Association for the Advancement of Colored People and the Congressional Black Caucus, both of which opposed the Thomas nomination. Board members confirmed the unanimous vote, and The Sun obtained the text of the resolution, which was not immediately made public.
The resolution specifically criticized Justice Thomas for his votes in three cases:
* A voting rights case in which Justice Thomas sided with the court majority in ruling that counties could shift duties from elected to appointed officials. Black elected officials contended that such a shift diluted the meaning of their election.
* A prisoner rights case in which the court said it was unconstitutional for prison guards to cause pain intentionally even if no serious injury to a prisoner resulted. Justices Thomas and Scalia dissented.
* A death penalty case in which the court barred prosecutors from using a convicted murderer's racist views and membership in a white supremacist prison gang as reasons to justify a death sentence. Justice Thomas was the lone dissenter. He argued that gang membership was evidence of "bad character" that could justify execution.
The SCLC said Justice Thomas showed in that case an "apparent willingness to undercut the First Amendment's guarantee of freedom of association, a bedrock principle for groups like the SCLC, in his zeal to uphold a death penalty sentence."
In addition to the Thomas resolution, the SCLC board charted other new courses at its semiannual meeting, reaching out to younger blacks and beyond traditional civil rights goals.
It voted a 25 percent increase in its $2 million budget to finance new programs in workers' rights, health care and family issues, voter education and "economic justice."
The Rev. Joseph E. Lowery, conference president, said the group would encourage blacks to deposit their money in minority-owned banks, and pressure banks to hire more blacks -- ranging from loan officers to board members -- to give minorities a better chance of getting loans.
Dr. Lowery called on the SCLC's 400 chapters to translate the group's national vision into local action. The group embarked this month on a national Stop the Killing Campaign focusing on black-on-black crime.
The SCLC, founded in 1957 by the Rev. Martin Luther King Jr. and others, has been criticized along with other civil rights groups as being out of touch with black Americans.
But Martin Luther King 3rd, the 34-year-old son of the late civil rights leader and an SCLC board member, said the group is "right on target . . . in going into communities to instill values and morals so young people will say no to guns and to violence."
Activist Dick Gregory, also a board member, said critics of the civil rights groups should join them. "If I'm dissatisfied with American Express, the first thing they ask for is my card number," he said. "People dissatisfied with the civil rights movement are not involved with it."