They should instead wear outfits inspired by “generalised characters and figures” such as ghosts, zombies and spiders.
“Let’s use our collective power to send a loud and clear message to our struck employers that we will not promote their content without a fair contract,” a spokesman for Sag-Aftra said.
The union also advised actors about not posting Hollywood-related costumes on social media as it issued its guidance on how to have a “strike-friendly” Halloween.
Members of the union have been on strike since July. Talks with the Alliance of Motion Picture and Television Producers broke down last week, dashing hopes for a resolution.
Meanwhile, George Clooney is leading a group of 15 A-list actors in putting forward a $150 million (£125 million or NZ$250 million) incentive to end the strike.
Earlier this week, the group proposed a no-cap fee on membership dues for higher earners, which they said would bring in up to $150 million over three years for the union, which could help fund improved health benefits.
The Oscar-winning actor also said top stars would only collect residuals - long-term payments for reruns - once lower-paid actors received theirs.
“A lot of the top earners want to be part of the solution,” Clooney told Hollywood publication Deadline, which first reported the news. “We think it’s fair for us to pay more into the union.”
The strike, which will mark its 100th day on Saturday, has disrupted film and television production, leaving thousands of crew members without work as well as the actors.
The Writers Guild of America ratified a new, three-year contract earlier this month, ending their 148-day strike.