Washington state is curbing the ability of parents to exempt their children from certain vaccines as part of a measure tackling a growing health crisis. Under legislation signed Friday by Gov. Jay Inslee (D), personal and philosophical objections by parents to vaccines for measles, mumps, and rubella will not be granted in the state.

“In Washington state we believe in our doctors. We believe in our nurses. We believe in our educators. We believe in science and we love our children,” said Inslee, also a 2020 presidential contender, as he signed House Bill 1638 into law. “And that is why in Washington state, we are against measles.”

More than 70 cases of measles have been reported in Washington this year, and an outbreak of the disease in the southwestern part of the state has cost public health officials nearly $1 million. Inslee declared an emergency over the outbreak and has moved to tighten vaccine laws. Of those sickened, 90% did not have the necessary vaccines to combat the disease. The outbreak itself lasted from January until April, taking a toll predominately in Clark County, where Inslee signed the bill on Friday.

Inslee has based his entire presidential campaign around climate action and science. He similarly pointed to established data and scientific findings in making his argument for vaccines this week, emphasizing the health benefits of relying on modern medicine.

“We should be listening to science and medicine, not social media,” the governor said. “So that’s why we need a national public health campaign about this issue, to make sure people across America get access to real science, based on real data rather than fear. It is science and truth that will keep us healthy rather than fear.”

Opponents of the new law protested outside as Inslee signed the bill. They argue that parents should be able to decide whether or not to vaccinate their children in keeping with religious beliefs and personal preference. Anti-vaccine activists have said they will continue to fight the bill and that they believe it imposes limitations on their personal health care decisions.

Washington allows for both medical and religious exemptions for attendance at public and private schools, in addition to day care, a caveat that will remain in place despite the new law. But lawmakers hope the new measures will protect against crises similar to the recent measles outbreak.

Health experts say vaccines are critical to protecting infants and young children from potentially deadly diseases, in addition to people with health issues that make them uniquely susceptible to illness. In 2015, a measles outbreak at Disneyland infected 20 people, leading California to abandon the state’s personal exemption laws. But other states have been slow to buck their own exemptions, a trend that could be changing now.

Tensions surrounding vaccines have exploded in the United States recently, thanks to the reemergence of diseases once considered effectively eradicated. By the end of last week, the Centers for Disease Control and Prevention (CDC) said there were 764 cases of measles currently in the country, concentrated in 23 states. And apart from Washington, 16 other states still allow for personal or philosophical exemptions with regards to vaccines, something that worries health officials.

The issue has also become partisan. President Donald Trump has argued that vaccines cause autism, something the CDC says is false. Republicans have also rejected Democratic efforts to tighten vaccine laws in several states, including Washington. Not a single Republican in the state Senate supported the bill signed Friday when it came up for a vote in April.

In states like West Virginia and Mississippi, meanwhile, some Republicans have sought to expand exemptions. Those two states are known for having strict vaccine laws, although all states technically have mandatory vaccination.

Vaccines and the exemptions afforded to parents have turned into a campaign issue as well. Earlier this month, BuzzFeed News contacted all then-declared 2020 candidates about their stances, most of whom expressed their support for vaccines. Mayor Pete Buttigieg of South Bend, Indiana, initially expressed support for exemptions, but then issued a “clarifying statement” emphasizing that the candidate “believes vaccines are safe and effective and are necessary to maintaining public health.” In a contrast, Sen. Elizabeth Warren (D-MA) said she supported ending both religious and personal exemptions.