This is more or less what I was trying to say with my original comment. Although unionizing is protected, "at-will employment" also leaves a lot of gray areas

This is more or less what I was trying to say with my original comment. Although unionizing is protected, "at-will employment" also leaves a lot of gray areas that can be leveraged for an employer to justify a termination. For example insubordination. The employer can claim that an employee was being hostile and creating a stressful work environment.