The Anti-Defamation League, a civil rights group that works against anti-Semitism and hate groups, wrote to Lieberman warning that too much talk about one's faith can be "inappropriate and even unsettling" in a pluralistic society, and "appealing along religious lines, or belief in God, is contrary to the American ideal."
Lieberman is not backing off. "I'm going to keep on doing what I'm doing because it's the American way," he said.
When Leiberman was rolled out as Gore's running mate in Nashville earlier this month,the senator praised God and quoted Scripture. He's never stopped mentioning the Supreme Being since. Repeatedly, he's referred to his candidacy as a "miracle" and spoken of his faith at most campaign appearances.
While concerned Jews have been discussing it for some time, apparently Lieberman's Sunday address to a black congregation in Detroit was the catalyst for the ADL's wrist slap.
Lieberman told worshipers at the Detroit Fellowship Chapel, "We need to reaffirm our faith and renew the dedication of our nation and ourselves to God and God's purposes." And he said he hoped his candidacy will help create "a place for faith in America's public life."
So what's wrong with that?
"If a Christian were making the kind of statements Lieberman is making, Jews would be frightened, outraged and upset," said Harvard Law School professor Alan Dershowitz. "And it doesn't make it kosher for a Jew to do it!"
"It would be the worst of ironies if it were a Jew who helped bring down the wall between church and state," said Dershowitz, who supports the ADL lettr. "Lieberman in effect has imposed a religious test: no atheists, agnostics or skeptics allowed. When George Washington said, 'We will no longer speak of toleration,' he meant that of agnostics and atheists too. Jews can never be guilty of opening the door just far enough to let ourselves in."
Alan Wolfe of the Boston College Center for Religion and American Public Life thinks the ADL's stand is "courageous" and "appropriate."
"I think Lieberman's right when he says he's not trying to impose his religion on anyone, but he may be opening the door to people who would want to impose their views on others."
But not every one agrees that Lieberman ought to leave the prayer shawl at home.
"Lieberman is not talking about Judaising America; he is talking about God," said Jack Wertheimer, a professor of American Jewish History at the Jewish Theological Seminary.
Wertheimer, who is "sympathetic" to Lieberman, adds the ADL had to speak out in the name of equal time. "The ADL have been quite militant in warding off incursion of the Christian right into American political life, and they have to demonstrate evenhandedness."
Voter.com's Randy Tate, a former executive director of the Christian Coalition, thinks the ADL letter is "very troubling."
"The political discourse would be hurt in this country if [Lieberman] was intimidated" into not talking about his belief, said Tate, who, as a former Republican congressman has policy differences with Lieberman.
"At a time when we're worried that every thing is focus-grouped and poll-tested, it's kind of refreshing" to listen to Lieberman, Tate said.
"It is one thing to say government should not favor one particular religious tradition over another," said Wertheimer. "It's a totally different matter to say individual American citizens should park their religious values at home when questions are being discussed that involve moral and ethical judgments."
Boston College's Wolfe said Jimmy Carter is the historical precedent for Lieberman.
Lieberman and Carter, he argued, are "similar politicians. And I mean that in a very positive way. In both cases, their faith gave them commitments to the public good. They're positive role models of how religion and politics can work together in an appropriate way."
"The question on which everything turns in America with religion and politics is: Does this appear to be a public or a private matter? Carter always made it clear this was his private faith."