Early on Woods had appeared to back the acting union's strike against the advertising industry, refusing to cross the picket line in the first days of the strike to shoot an ad for Nike. But that has changed.

"Obviously, this is going to be bad news if he is doing this spot," a SAG source told the trade magazine.

At a strike rally on Wednesday, SAG chairman Todd Amorde addressed the issue, asking Woods not to shoot the commercial.

"Right now, General Motors and the Buick Motor Division are trying to convince Tiger Woods to cross the line up in Canada. They're telling him it's ok it shoot a spot up in Canada. Well, we're here to tell you, Tiger, that it's not ok. Say it isn't so, Tiger."