The American Humanist Association applauded Rep. Pete Stark for publicly acknowledging he does not believe in a supreme being. The declaration, it said, makes him the highest-ranking elected official - and first congressman - to proclaim to be an atheist.
The organization took out an ad in Tuesday's Washington Post, congratulating the California Democrat for his stance.
"With Stark's courageous public announcement of his nontheism, it is our hope that he will become an inspiration for others who have hidden their conclusions for far too long," executive director Roy Speckhardt said in a statement.
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Stark's beliefs garnered attention after the Secular Coalition for America offered a $1,000 prize to the person who could identify the "highest level atheist, agnostic, humanist or any other kind of nontheist currently holding elected public office in the United States."
Associate director Ron Millar told the Los Angeles Times that the group wanted to highlight the difficulty that politicians have declaring they don't believe in God.
A member of American Atheists California nominated Stark.
"We didn't think we'd have any member of Congress come forward," Millar said.
Stark, whose district is in the San Francisco Bay-area town of Fremont, confirmed his belief in a statement to The Associated Press late Monday. He said he was "a Unitarian who does not believe in a supreme being."
"I look forward to working with the Secular Coalition to stop the promotion of narrow religious beliefs in science, marriage contracts, the military and the provision of social services," he wrote.
Unitarian Universalism describes itself as creedless, allowing members to shape their beliefs based on personal experience rather than an authoritative statement of religious belief. Some members believe in God, but not all do.
Stark has represented Fremont in Congress since 1973 and chairs the health subcommittee of the House Ways and Means Committee.