The Wikipedia definition is more apt here, and solves the confusion that you're having:

> Extortion (also called shakedown, outwrestling, and exaction) is a criminal offense of obtaining money, property, or services from a person, entity, or institution, through coercion.

It's not a criminal offense when the government is doing it legally, which they are in this case because the legislature passed a law through the normal process.

Do you call all taxation "theft" as well?