Employer Says My $80k Offer Was A "mistake" After 8 Months—but Only After I Disclosed I Need Surgery.

Location: Idaho

I'm hoping someone can tell me if I'm overthinking this or if I should be more careful before agreeing to anything.

About 8 months ago I accepted a job after getting an emailed offer letter for $80,000/year salaried. I accepted it by email, left my old job, and have been working there ever since. It's a position they basically created for me, so there's nobody else doing the same job.

A couple of weeks ago I told my boss that I have surgery coming up, and we started talking about what work would look like while I recover.

Out of nowhere, I was told they recently realized my position was "supposed to be hourly" the whole time. They said they made a mistake when they hired me and now want to switch me to $35/hour permanently.

What throws me off is that this somehow wasn't caught during hiring, onboarding, payroll, or anytime in the last eight months. It only became an issue after I mentioned needing surgery.

They also told me the hourly rate takes PTO into account, but I've already been earning and using PTO this entire time as a salaried employee.

Nothing has been put in writing besides my original offer letter. I sent my manager an email afterward just to make sure I had a record of what we discussed, and he replied saying we'd talk more in person.

I'm not trying to sue anyone or start a fight at work. I actually like my job. I just don't want to walk into this meeting and accidentally agree to something I shouldn't.

Can they legally do this in Idaho? Does the written offer letter matter at all, or can they just say it was a mistake and change my pay going forward?