An employee at T-Mobile sent out a companywide communication asking her coworkers to support the Communication Workers of America. The employee sent the email while on her break and told employees to reach out to her after work hours if they had any questions. The employee’s supervisor and team leader met with her and told her that this was all prohibited. The union filed an unfair labor practice charge. An administrative law judge found T-Mobil guilty of several violations, the NLRB ruled just that they had violated Section 8(a)(1) of the NLRA, so the union petitioned the D.C. Circuit for a review and now the decision of the NLRB has been reversed and sent back to the NLRB.
See "Disciplining an employee for mass pro-union emails to coworkers violated the NLRA", Jeffrey Rhodes, SHRM, October 5, 2021