And, if you work for any publicly traded company, and have access to material non-public information, then the exact same rule would apply.
Suppose you work for a company, and you tweet information about your company that has not been disclosed publicly through a formal press release, and which contains information that would cause someone to estimate the value of the company differently. If someone reads that, and makes an investing decision based on it (they buy, or sell, or short stock in your company) then, boom, you just broke the law by improperly releasing that information. If you disclose it to a small group of friends (say your Facebook circle), then they have you (and your friends) for insider trading. It won't just get you fired, it'll put you in jail.
Nothing about this is peculiar to brokerages.