Starbucks did the same thing, arguing that -

“Wages and benefits are mandatory subjects of the collective bargaining process,” the company said. It rejects the union’s argument that it could offer the wage and benefit enhancements to unionized stores at any time.

The NLRB countered -

"...the NLRB said Starbucks violated labor law by offering raises and benefits — including increased training, career development opportunities, expanded tipping and even looser dress code policies — only to nonunion stores."*

Source: https://www.seattletimes.com/business/starbucks-shortchanged..., @ https://archive.ph/CrZTh