"The NLRB complaint also seeks an order requiring that Amazon publicly post the NLRB explanation of employee rights for one year; provide laid-off workers with a “neutral letter of reference” that says their performance was “satisfactory” and does not mention “the circumstances surrounding their termination of employment”; permit the NLRB to train management on unfair labor practices; and provide the regional board director with written proof of compliance."
I'm sympathetic to unions, but its pretty obvious why a First Amendment argument tracks.