Why would I be going from salaried to hourly by the new law?

I make under $48,000. I was told by my boss I might be going hourly (this was before the law passed). I barely work any over time (35–37.5 hrs/week) and have 20 days PTO and sick time. If I were to be hourly it would go down to 10 days PTO. She said I would be grandfathered in to keep my benefits.

So why would I become hourly if I don’t have over time? I work at a university and we many staff that are three quarter time (salaried and working 10 months but paid cover 12) and they would become hourly apparently too.