It's often described as a law that requires you to move over from the right lane to the center lane if there's a car or an emergency vehicle on the shoulder with their Emergency Flashers turned on.
HOLY CRAP I've seen people suddenly try to move into the center lane, squeezing between other cars, slamming on their brakes, forcing other cars to slam on THEIR brakes. CRAZY!!!
The law is actually the "Move over OR SLOW DOWN" law.
If there's too much traffic to safely move over, you CAN just slow down.
I've seen that misunderstood law come SO CLOSE to causing serious collisions.