Two things:
1. By law, no person is required to pay union dues.
2. Right-to-work means they don't even have to pay "agency fees" which are the cost of bargaining/representation and have nothing to do with politics or political campaigns.
So what is right-to-work?
Under
U.S. labor law, a union that wins an election in a workplace must represent all the workers in the bargaining unit, even the ones who may have voted against the union. Since that representation costs money, unions prefer to ink contracts that require all the workers in the unit to support the union financially. Right-to-work laws make such arrangements illegal.
Under right to work, no employee can be required to pay fees to the union. Once provided with an out, many workers naturally choose to stop supporting it. Some may have never liked the union or its politics. But others may opt out simply due to economic self-interest: It makes little sense to pay the union for a service that it's obligated to provide you anyway.
Conservatives like to say right-to-work legislation promotes individual freedom. Unions like to say it advances individual
free-riding, since workers can enjoy the benefits of the union's bargaining without helping to underwrite it.
(Contrary to popular opinion, no worker in the U.S. can be forced to be a full dues-paying, card-carrying member of a union. But they can be compelled to pay so-called "agency fees" -- the portion of dues that goes expressly to bargaining and representation costs, as opposed to, say, political campaigns. Right-to-work guarantees that workers do not have to pay these fees.)
On the right, proponents of right-to-work argue that the laws make states more competitive and attract business. On the left, opponents of right-to-work argue that the laws drive down wages and fail to create jobs. What few would deny is that right-to-work laws can be crippling for organized labor.
As workers bow out of unions, the remaining workers must bear a larger share of the costs associated with representation and organizing. And if the union becomes less effective, workers have even more reason to leave, creating a downward spiral.
More:
How Right-To-Work Laws Hurt Unions
It doesn't take a genius to see the obvious union-busting intent of RTW.