By Gina Cherelus and Laila Kearney

NEW YORK, June 12 (Reuters) - Actors and other artists threatened on Monday to boycott Delta Airlines and Bank of America after they pulled their sponsorships of a New York production of William Shakespeare's "Julius Caesar" that portrays the assassinated Roman leader as U.S. President Donald Trump.

The companies ended their support of the production by the nonprofit Public Theater on Sunday. The move came hours after Trump's son Donald Jr. in a tweet questioned whether it was art or political speech.

"Disappointed in @Delta for turning its back on free expression. I've flown many thousands of miles with you. No more," Beau Willimon, an American playwright and creator of the popular Netflix series "House of Cards," wrote on Twitter.

Novelist Joyce Carol Oates tweeted that she would see the play "in thrilled defiance of ignorant would-be censors."

Actor Ron Perlman, known for his big screen depiction of "Hellboy," also condemned the two ex-sponsors.

"Act accordingly," Perlman told his followers on Twitter.

Delta Air Lines Inc and Bank of America Corp also received support on social media.

"Kudos to @Delta for pulling $$ from 'play' portraying assassination of @POTUS. No one should sponsor crap like that!" Arkansas Governor Mike Huckabee, a Republican whose daughter is deputy White House press secretary, wrote on Twitter.

It was not immediately clear why the companies withdrew their support more than two weeks after the play opened on May 23 as part of its Shakespeare in the Park program in Manhattan's Central Park. Company representatives did not respond to requests for comment.

The Public Theater did not respond immediately for comment.

"I wonder how much of this 'art' is funded by taxpayers? Serious question, when does 'art' become political speech & does that change things?," Donald Trump Jr. wrote on Twitter on Sunday morning after seeing a Fox News story about the play.

Author and journalist Summer Brennan said adapting Shakespeare's work to different eras was a longstanding theatrical tradition.

She said she had seen of the 16th century playwright's pieces set in different eras, including World War One and Two, the American West, a health deaura spa, and in outer space.

"Setting Shakespearean political tragedies and history plays in current or recent administrations is an important tradition. #DontBanTheBard," Brennan wrote on Twitter on Monday.

American Express Co, which calls itself "the official card of The Public Theater," said on Monday it did not support this version of "Julius Caesar," but did not say if it would drop funding.

"The Public Theater puts on many shows. Our sponsorship does not go toward the funding of the production of Shakespeare in the Park and we do not condone this interpretation of the play," American Express said in a statement.

Delta and Bank of American ended their sponsorships less than 12 days after comedian Kathy Griffin faced a backlash after posing for a photograph with a fake severed and bloodied head resembling Trump.

After images were published on social media, Griffin lost sponsorships and jobs, including co-host of CNN's New Year's Eve coverage. (Editing by Jeffrey Benkoe)