History clearly shows...
In the gun vs armor race, the gun always wins. Mounted knights of old, modern tanks, police vests, it matters not. There is always a gun powerful enough (or a bow) to penetrate the armor.
This is a bad concept and would make a bad law, especially as open ended as it is written. Isn't already a crime to shoot police officers (vests or no vests?)? If that isn't enough law to prevent it happening, what good does one more law do? And what about icepicks and screwdrivers?
All else being equal (and it almost never is) bigger bullets tend to work better.