It also is in the US, but apparently it is a common trope by anti-union politicians to act like this isn't already law.
Yes, technically you don't have to join unions anywhere in the US. If you want, you can give up your membership and benefits, but still have to pay dues. Obviously, that's really one-sided, which is why a few states (but not the whole US) have passed right-to-work laws.
Federal law forces US unions to represent non members. "Right to work" laws force unions to do it for free in most states. The rest allow unions to charge agency fees to cover the mandated services. Not full dues.