By Hilary Russ

NEW YORK Pro-union baristas at Starbucks are taking their campaign on the road on Monday and trying a new tactic along the way: asking the coffee chain's customers to organize pickets at non-unionized U.S. cafes.

The Workers United union plans to hand out flyers during a 13-city bus tour to customers with a QR code that takes them to a sign-up sheet to organize their own protests during a "national 'Adopt-a-Store' day of action" on Aug. 7, according to copies of the flyers seen by Reuters.

The union is taking a more aggressive tactic of directly targeting customers as contract negotiations drag on. The union and company blame each other for bargaining delays and alleged labor law violations.

Starbucks has been accused of more than 570 unfair labor practice charges. On Thursday, the National Labor Relations Board sued Starbucks over its refusal to rehire 33 workers as it shuffled three downtown Seattle stores into its "Heritage District" after one of those cafes unionized.

The dispute is threatening Starbucks' reputation as a progressive employer, with some investors pressuring the company to account for its treatment of pro-union employees.

The union now represents baristas and shift supervisors at about 320 of Starbucks' roughly 9,000 corporate-owned U.S. locations. However, its recent growth is at risk if it cannot reach deals at the stores where it represents employees.

"Despite the fact that we have attempted to schedule bargaining for hundreds of stores, Workers United has only met Starbucks at the table to progress negotiations for 11 stores," Starbucks said in a statement.

"(Employees) voted for bargaining not buses," the company said, adding that stalled negotiations have led workers to be so frustrated that they filed petitions to kick out the union at several stores.

The union's tour has two legs: one travels through the Midwest, South and East, while a second leg will run up the Pacific coast, arriving in Seattle around Aug. 7, the union said.

The tour will also target Starbucks board members such as Land O'Lakes CEO Beth Ford, whose likeness was carved into a statue made of butter that union members delivered to the creamery's Minneapolis headquarters in April.

(Reporting by Hilary Russ; Editing by Richard Chang)