Unlike the U.S. Constitution, California's governing document includes an explicit guarantee of the right to privacy. Yet the Golden State's Supreme Court ruled last week that the guarantee is waived if a union wants to send somebody to a person's front door to explain why he should stop causing trouble and hand over money for union dues -- if he knows what's good for him. Or words to that effect.

The implications are chilling and ought to serve as a reminder to lawmakers in the 26 states without a right-to-work law that they should adopt one, soon. In the meantime, the California case pitted Los Angeles County against the Service Employees International Union. California has no right-to-work law, so the county government's employees have no choice but to either join SEIU or at least pay dues to it. They can object if their dues money is spent on political campaigns, but few do so for fear of workplace retaliation.

For many years, the county government acted as go-between for the union and the non-members by collecting dues. Then in 2006 the SEIU demanded that county officials turn over all workers' contact information. The court ruled on May 30, 2013, that, since the union's contract requires it to represent all county employees, it can contact them as well.

The court acknowledged that workers who opted not to join the union have "enhanced" privacy rights, but still ruled that the union's interests trump individual rights. But the ruling ignored the fact that the only reason the SEIU represents all county employees is that the union insisted on it in contract negotiations with local officials. Nothing in California or other law prevents the SEIU or other unions in California from signing contracts that obligate them to represent only dues-paying members.

The practical effect of this unfortunate ruling is that the SEIU now has a list with contact information for every employee that has opposed the union bosses' political agendas and favored candidates. Still, the logic underlying the ruling is plain: If the judges allow contracts so titled in the unions' favor, then they should also remove obstacles preventing labor officials from enforcing the agreements.

Workers everywhere should pay heed. The political battles over workplace rights are intensifying. While traditionally labor-friendly states like Indiana and Michigan have embraced right-to-work laws, labor leaders have been quietly shoring up forced-dues unionism in others. That's why, for example, Maryland recently added teachers to an existing law requiring all state employees to pay union dues.

For Big Labor, preserving such arrangements are crucial. Much of their power stems from their ability to force people to join up or at least pay dues. After Wisconsin amended its laws in 2010 to allow state employees to opt out of joining, the state's public sector unions lost between a third and a half of their members. So union leaders know how damaging such reforms can be. With unionization down to 11.3 percent of the workforce nationally, they cannot afford further losses. So the fight will only get rougher. That doesn't mean it isn't worth fighting. The right to feel safe in your home is as fundamental as it gets. California proves Big Labor bosses will take it away if given a chance.