Lethal Weapon star Danny Glover has accused pressure groups in the United States of "rabid nationalism" after they criticised his political views.
Glover went on anti-war marches in the US
A group called Judicial Watch has urged a boycott of telecommunications company MCI, which Glover advertises.
Judicial Watch said they were "repulsed" after Glover signed a statement criticising US policies towards Cuba and Iraq.
In reply, Glover said right-wing factions had become the self-appointed thought police.
"It's basically this rabid nationalism that has its own kind of potential of being maniacal," he said.
"As we march down and wave the flags, we must be sure of what we're waving them for."
Something is happening now that is very dark and very sinister in this country
He accused groups like Judicial Watch of wanting to "crush any kind of dissent".
"Something is happening now that is very dark and very sinister in this country, and for us to not admit it is happening is, in some ways, for us to be blind," he said.
Before the military assault in Iraq, actors' union Screen Actors Guild warned that anti-war actors could be blacklisted.
Martin Sheen, Sean Penn, Tim Robbins, Susan Sarandon and country group the Dixie Chicks have all come under fire for speaking out.
The statement signed by Glover and 159 other people, addressed to The Conscience of the World, appeared in Cuban government newspaper Granma.
It said the Iraq war was an unprovoked, unjustified invasion and there was "a strong campaign of destabilisation" against Cuba that could be used as "a pretext for an invasion".
Glover is coming out in support of a terrorist murderer, Fidel Castro
Judicial Watch president Tom Fitton said MCI endorsed Glover's views by giving him work.
"Glover is coming out in support of a terrorist murderer, Fidel Castro," Mr Fitton said.
"People who are against murder and torture are repulsed by his support, and MCI is slow on the uptake."