01/18/2007 AT 09:55 AM EST
A gay advocacy group is demanding that Grey's Anatomy'
s Isaiah Washington apologize for calling co-star T.R. Knight a "faggot" last year and then repeating the word at the Golden Globes.
Neil Giuliano, president of the Gay & Lesbian Alliance Against Defamation, said Wednesday he had contacted Washington's camp in hopes of discussing "the destructive impact of these kinds of anti-gay slurs" with the actor, the Associated Press reports.
Giuliano said in a statement: "Washington's repeated use of (the slur) on-set and in the media is simply inexcusable."
Washington's publicist declined comment Wednesday, according to the AP.
Washington reportedly used the slur during an on-set argument with Patrick Dempsey
in October in reference to costar T.R. Knight, who later revealed that he is gay.
After the Golden Globes on Monday, Washington denied the incident, telling reporters, "No, I did not call T.R. a faggot. Never happened, never happened."
Knight appeared on The Ellen DeGeneres Show
on Wednesday, where he said Washington's slur gave him the courage to come out
. He added that he was mystified by Washington's denial. "He referred to me as a faggot," he told DeGeneres. "Everyone heard it."