Where I worked in Europe I don't think it's considered a "fireable offense", but it's definitely something you tend not to share with coworkers, and it would be

Where I worked in Europe I don't think it's considered a "fireable offense", but it's definitely something you tend not to share with coworkers, and it would be frowned upon by your boss/HR. On the other hand, it's not uncommon to share it between friends or ex-coworkers. Salaries also tend to vary wildly, and are not necessarily linked to seniority. The best way for a junior to rapidly increase his salary is to change jobs, or threatening to change jobs and receiving a counter-offer.