What right-to-work does, essentially, is allow people to enjoy the benefits of a union without having to pay union dues. The union is required to advocate on behalf of all employees at the workplace, not just those who have joined the union, but this means that people can freeload on what the union does... which means more and more people won't bother to join the union... which means the union collapses... which means that all the workers get a shittier deal because there's no union to negotiate on their behalf.
But, again, I'm not sure if, constitutionally, the federal government can pass a law to preempt state-level right-to-work laws.