> People will make out hiding salaries is some grand conspiracy

In the US, the National Labor Relations Act covers this situation. The NLRB says that discussing wages/salaries is a covered "labor organizing activity" and it is a violation of the NLRA to prevent employees from discussing wages.

> If you are an employee covered by the Act, you may discuss wages in face-to-face conversations, over the phone, and in written messages. Policies that specifically prohibit the discussion of wages are unlawful as are policies that chill employees from discussing their wages. When using electronic communications, like social media, keep in mind that your employer may have policies against using their equipment for unauthorized use, though it is possible such policies could be unlawful.

> You may have discussions about wages when not at work, when you are on break, and even during work if employees are permitted to have other non-work conversations. You have these rights whether or not you are represented by a union.

https://www.nlrb.gov/about-nlrb/rights-we-protect/your-right...

29 USC 151-169 is the NLRA:

https://www.law.cornell.edu/uscode/text/29/chapter-7/subchap...

https://en.wikipedia.org/wiki/National_Labor_Relations_Act_o...

NLRB:

https://en.wikipedia.org/wiki/National_Labor_Relations_Board