Federal law protects employees engaged in union activity, but that's only part of the story. Even if you're not represented by a union - even if you have zero interest in having a union - the National Labor Relations Act protects your right to band together with coworkers to improve your lives at work.
You have the right to act with coworkers to address work-related issues in many ways. Examples include: talking with one or more co-workers about your wages and benefits or other working conditions, circulating a petition asking for better hours, participating in a concerted refusal to work in unsafe conditions, and joining with coworkers to talk directly to your employer, to a government agency, or to the media about problems in your workplace. Your employer cannot discharge, discipline, or threaten you for, or coercively question you about, this "protected concerted" activity. However, you can lose protection by saying things about your employer that are egregiously offensive or knowingly and maliciously false, or by publicly disparaging your employer's products or services without relating your complaints to any labor controversy.