The Guild said the writers of "Good Night, and Good Luck" were chosen for their film's portrayal of constitutional and civil rights.
"This smoke-filled black and white film is a crystal clear and colorful validation of why news media must be free and independent from both political and corporate whim and intimidation," WGAw President Patric M. Verrone said in a news release. "It is as relevant today as it was when the events themselves happened more than 50 years ago."
Clooney and Heslov not only wrote the film, but they produced it. Clooney directed and acted in it as well.
The award will be presented during the 2006 WGA Awards Feb. 6 in ceremonies in Los Angeles and New York.