George Clooney has quietly withdrawn from the Writers Guild of America after the union rejected his request for a writing credit on his new film “Leatherheads,” Daily Variety reported in its Friday edition.

Clooney opted to become a “financial core status” nonmember last fall, which means that he is still covered by the basic contract, the trade paper said.

But he loses his voting rights, and cannot run for office or attend membership meetings, according to the WGA’s constitution. He must continue to pay his dues, but gets a break on “non-germane” WGA activities, such as political and lobbying efforts. His decision is also irrevocable.

Clooney, 46, directed, produced and stars in “Leatherheads,” a screwball period football comedy that opens across North America on Friday via General Electric Co’s Universal Pictures. Despite mixed reviews, it is expected to be the top draw at the weekend box office.

He had sought to receive a writing credit alongside Duncan Brantley and Rick Reilly, claiming that he personally gave the duo’s languishing 17-year old project a major overhaul.

Clooney, who received an Oscar nomination two years ago for co-writing “Good Night, and Good Luck,” told Daily Variety that he felt he had written all but two of the scenes for “Leatherheads.” His request for credit was voted down 2-1 at an arbitration hearing.

“When your own union doesn’t back what you’ve done, the only honorable thing to do is not participate,” the paper quoted Clooney as saying.

He said he would have resigned from the union altogether — a revocable move — but that would have prevented him from working on all WGA-covered productions. He kept quiet about his move, because the union was about to go on strike for the first time in almost two decades, and he did not want to provide an unwelcome distraction. Clooney was a keen supporter of the 100-day strike, which ended almost two months ago.

The WGA did not comment for the Daily Variety story, and a union spokesman did not immediately reply to an e-mail seeking verification of the report.