The Screen Actors Guild (SAG) said a slew of hate-mail directed at actors who have taken a public personal stand against war, along with calls for boycotts of movies and albums on the nation's talk radio airwaves and Internet message boards, "suggests that the lessons of history have, for some, fallen on deaf ears."

"We deplore the idea that those in the public eye should suffer professionally for having the courage to give voice to their views. Even a hint of the blacklist must never again be tolerated in this nation," SAG, the nation's largest actors' union, said in a statement.

The SAG statement was issued in response to a growing tide of abuse toward American celebrities who have spoken out against a "rush to war" on nationally televised award shows, through interviews, anti-war TV ads or by taking part in mass protests.

Martin Sheen, who plays TV's popular fictional President Josiah Bartlet on NBC's "The West Wing," has been under fire since emerging as a chief spokesman in the anti-war coalition. Sheen said in a Los Angeles Times interview this week that his hate-mail critics have demanded that NBC fire him from the Emmy-award winning series, adding that NBC executives had privately expressed fears that ratings would suffer because of the furor.

Sheen said the show's staff has been "100 percent supportive" but that top network executives have "let it be known that they're very uncomfortable with where I'm at."

NBC said on Tuesday that Sheen's personal views had nothing to do with the show. "Martin Sheen is acting in his capacity as a private citizen. We respect his opinion and his right to freedom of expression," NBC said in statement.

SAG said suggestions that "well-known individuals who express 'unacceptable' views should be punished by losing their right to work" was a "shocking development" which recalled the 1950s House Committee on Un-American Activities under Senator Joseph McCarthy.

More than 320 people, including Arthur Miller, Orson Welles, Dashiell Hammett, Paul Robeson and Charlie Chaplin were placed on a blacklist that stopped them working for the entertainment industry because of views considered left-wing or unpatriotic.

SAG called it a "shameful period" for the entertainment industry, saying the industry today had a duty to guard and cherish U.S. constitutional principles of free speech rather than "prostrate itself before smear campaigns and witch hunters" as it had 50 years ago.

Sheen, along with actor Sean Penn (who visited Baghdad in January), singer Sheryl Crow (who performed at last month's Grammy awards wearing a "No War" guitar strap), and scores of other celebrities have been slammed for being unpatriotic.

"I will not go to the movies. I will not support their television shows, I will not buy their music. My family and I shall boycott supporting anyone in Hollywood until they decide their job is for entertainment value only," said one writer to the "Citizens Against Celebrity Pundits" online petition. G.I.Jargon.com, a Web site representing U.S. military, police and firefighters, dubbed the celebrities "Taliban" and called for a boycott of "anti-American entertainers."

McCarthyism expert Ellen Schrecker, professor of history at Yeshiva University in New York, said the level of rhetoric against anti-war campaigners could presage a return to the era of witch-hunts and blacklists.

"I think it is certainly a possibility. What I find heartening about the SAG statement is that it recognizes the importance of remembering that history, and being determined not to repeat it. "It's very important to take a public stand the way the SAG has done," Schrecker told Reuters.