There’s a lot of controversy surrounding mandatory childhood vaccinations. While the majority of people — including most medical professionals — believe that immunizations are important, there is a highly vocal minority of “anti-vaxxers” that believe that vaccinations are dangerous.

Unfortunately, the anti-vax movement is leading to problems. Many young children and people with compromised immune systems rely on “herd immunity” to protect them from diseases like measles, mumps and chickenpox. When not enough people have been vaccinated, outbreaks of those preventable diseases start to happen. In some instances, children have died from what are largely preventable illnesses.

Back in 2015, California took action. A law was passed that ended parents’ ability to exempt their child from vaccinations simply by stating personal or religious beliefs. Now, children are required to have medical approval in order to gain an exemption.

Some physicians saw an opportunity. Those willing to market their services to anti-vaxxers have even advertised their services on social media, offering exemption evaluations in exchange for cash.

Another law is about to tackle that kind of behavior. Senate Bill 276, which is sponsored by Senator Richard Pan (who is, himself, a pediatrician and the legislator that pushed for the 2015 law), would standardize the request forms for vaccine exemptions and require all completed forms to go through the state’s health department. Currently, there is no standardized form and no systematic review process in place.

Experts say that despite efforts to limit vaccination exemptions for personal and religious reasons in California (and a few other states), the number of medical exemptions granted has quadrupled. While there are legitimate medical reasons to exempt a child from vaccination, they’re very limited.

Officials believe that some physicians are essentially selling their signature on exemption forms for the right price. For example, an investigation into a San Diego school district found that more than 100 exemptions — around a third in the district — were all signed by the same physician.

It’s important to note that the new law is backed by the California Medical Association. That means that physicians need to be wary about signing vaccine exemptions — even when pressured by parents — if they aren’t medically necessary. Doing so could eventually lead to an investigation into a physician’s ethics.