Ask HR: Military reserve status does not need to be disclosed to a potential employer

While it may not be required, it can be advisable to do so just in case something happens. Employers tend not to like surprises.

I let my employer know up front that I was in the reserves, there was no issue with it.

I had no issue with telling employers of my IRR status when I first separated from active duty. I explained if WWIII happened I would get recalled back to active duty. A couple years later when I decided to go into active reserves I again told my employer of my decision and that only my 2 week commitment a year would impact my job. They had no issue with that, my manager was a veteran so that may have made it easier.