A community of 30,000 US Transcriptionist serving Medical Transcription Industry
discuss your pay in public as much as you would like. It is the law. It does not matter if you have signed a nondisclosure statement on salary as that is not legal. If you are fired for talking about your salary you have legal grounds for compensation.
Of course distributing copyrighted material is illegal, but you can talk about your work concerns and salary in public. It is the law no matter what a company tells you.
You do not have to be part of a union. You have rights as an employee and an American citizen and this is one of them.