Unemployment taxes for a company scale based on historical claims from that company. More Unemployment Benefits paid out = more future UI taxes paid by that employer. It's meant to be a self-funding system.

To expand on what phonon said -- UI tax rate is company specific and depends, in part, on how much UI is paid out to company's employees.

That sounds a nightmare of bureaucracy to calculate!

I mean, that’s how most insurance premiums work.