Almost every company encourages their employees to never disclose their pay to their coworkers. It promotes an information imbalance where the employer wins. Unless you sign something saying that you won't disclose it (which would probably be contestable anyhow), or you're sharing it with someone who doesn't want to know (which would just be rude and potentially disruptive), they can't fire you for telling people what you make.
Don't do it, plain and simple. If you didn't agree to keep it a secret, then it's not a secret. With all of my raises and bonuses-that-not-everyone-gets, I was discrete, just as my bosses asked of me. I only share my compensation information with anyone and everyone who wants to know. It's time we changed this stupid "secret salary" custom.
Also, promotions and raises aren't given, they're taken. You're a grownup, why should your employer care more about your career than you do? Want a promotion? Take more responsibility. Be more essential. Be a leader. Want a raise? Get a better offer, and ask your employer to match it. Write essays, share code, increase your skillset, help your juniors, always be finding ways to make the product better, ways to make the team's processes more efficient.
If you just want to do your job and stay warm, that's fine, but don't expect to get special treatment. A yearly 2-7% cost-of-living pay increase is probably about right.
It sounds harsh, I know, and I'm sure this might not have been your angle at all. I just get annoyed hearing about employees who dutifully do no more than they're told, and wait and hope for review time as if it's christmas, and then get upset when they're treated like cogs in a machine, when they've been acting exactly like cogs in a machine.
Yes they can. Unless you are talking about Western Europe or something.
To be clear, in California at least, you can be fired or quit for any or no reason whatsoever. So, yes, to correct what I said, an employer could fire you for sharing your salary, or for the car you drive, or for the color of your hair, or just because they don't like you for no specific reason. (But not for your gender, race, disabilities, or religion. Doesn't that seem odd?)
However, very few employers will fire you for this. And, if they're that serious about keeping their employees in a disadvantageous position, maybe you ought to find a more respectful employer.
So, how much do you make? ;~)
Sorry, that was kind of awkwardly phrased. Should have reread before posting.