In Los Angeles on this May Day, the actors who make commercials for radio and television are going on strike. It’s the first major Hollywood strike since writers walked off the job 12 years ago. The 135,000 actors belong to the Screen Actors Guild and AFTRA, the American Federation of Television and Radio Artists. Advertising companies want to scrap the network fee system that pay actors every time an ad runs; instead, they want to adopt the flat-rate pay system used for cable commercials. No talks are scheduled. Agencies say they’ve been stockpiling commercials in anticipation of a strike, and they’ll try to produce new ads using nonunion actors.