Wrong. That's just factually and irrefutably wrong, it's a lie spread by unionistas to pretend they're being unfairly asked to support even those who don't belong.
Unions have the option of establishing contracts for exclusive representation or not. If they choose to establish the contract for exclusive representation, then they become the ONLY entity that the employer can negotiate with on behalf of any employee (union or non-union), and thus, the non-union employees also receive the benefits of whatever the union negotiates. They union has the option of not having exclusive representation, in which case they do not have to represent anyone not in the union, and anyone not in the union doesn't have to get the same wages/benefits/representation union members get.
They can either choose exclusive representation and have to deal with free riders, or choose non exclusive representation and not have free riders.
Again, nobody is demanding union protection without paying for it. The union itself mandates that issue because of exclusive representation contracts.