I know of no federal bill or law. Kansas is a "right to work state".
So in Kansas no one must belong to a union nor be required to pay dues.
Those of us who do belong carry the others because the union bargains
for all the teachers and everyone receives the same benefits. Missouri
on the other hand is not a "right to work state" and unions can require
that employers collect dues from everyone in the bargaining unit. My
wife is union and works in Missouri. We are right on the state line and
many work in one state and live in another.
Happy to pay my share, Woody in KC