This is such a difficult situation. Your health comes first, and don't worry for a second about what might happen to your employer in negative situations. But

This is such a difficult situation. Your health comes first, and don't worry for a second about what might happen to your employer in negative situations. But the issue would be difficult to navigate for someone very familiar with the details. 'Legality' may be of secondary concern here unfortunately - you may be entitled to certain rights, but often companies just don't care and will screw you, leaving you with no choice but to sue etc. - nobody wants to deal with that. It's rational for them to not necessarily want to pay you more, even for ostensible promotions, but it doesn't mean they don't value you. Also - consider that everyone is human on some level, you may want to let them know you have to go in for some kind of surgery without disclosing any of the details at all. You may want to indicate that you can have your Doctor contact them. This may seem odd, but maybe you literally want to get a Doctor's note which indicates the seriousness and recovery time without getting into any details. The Doctors note will legitimise the situation so they'll 'have no doubts' - and with that documentation on file, they'll think twice about doing something screwy: if you end up in small claims and a Judge sees they have something like that on record, it can't be good for them. Maybe once you've let them know, you can try to judge from their response the level or career risk you face. You can perhaps offer to 'work out a time' with them if that's an option for you. It can't hurt to put out the feelers for another job as well. Good luck with your situation. Life is long, your health is the priority. In the long run, if you find that you're seriously in a situation wherein your company won't cut you some slack for something so serious, then it's almost definitely time to move on. Good luck.