Persuading audiences to care is at the heart of an unusual new crusade in Chicago that may soon spread to other big theater towns. Actors’ Equity Association, the union for performers on Broadway and at theaters nationally, began an online publicity campaign in September to educate people about the differences between Equity tours and cheaper nonunion tours, in hopes of pressuring bookers to present more of the Equity type and that way increase the number of union jobs.

The 50,000-member Equity has spent a low five-figure sum on the campaign, chiefly to buy online ads that encourage people to ask ticket sellers and others if productions are Equity tours. The ads pop up on Hot Tix and other Chicago ticketing websites, as well as on popular blogs like The Chicago Tribune’s Theater Loop.

“The word ‘Broadway’ gets used a lot by touring shows in cities across the country, but some of them have nothing to do with Broadway — so why are audiences paying as much for them as they would for Broadway shows?” said Mary McColl, the executive director of Equity. “I think a lot of audience members are discerning, and we’re asking them to vote with their feet.”

The campaign is partly a response to the continuing threat that Equity leaders see from nonunion tours: There are about 20 moving around the United States at any one time, compared with about 25 Equity tours. Equity once had a bigger share of the market, but the growing expenses of producing shows — and the unpredictability of ticket sales — have led to more lower-cost nonunion tours.

Equity tours are typically based on recent Broadway productions, and actor salaries range from $550 to $1,850 a week, plus per diem. Nonunion tours usually come with lower salaries, smaller production budgets and frequent travel days among cities; they are often based on older Broadway productions (like “Annie”) or are unrelated to Broadway, like the “Evil Dead” tour that also ran here this fall.