Tesla’s ban on clothing with union logos is unlawful, the National Labour Relations Board has declared, effectively making it more difficult for employers to restrict workers displaying their support for unionisation amid a surge in labour organisation nationwide.

The electric car manufacturer’s “team-wear” policy requiring employees to wear a plain black t-shirt or one with the Tesla logo effectively prevented workers from wearing a shirt with a union insignia, the NLRB said resolving a long-running dispute from 2017.