State legislators across the country are moving to tighten limits on vaccine exemptions for children amid one of the worst outbreaks of preventable diseases in recent history.

Legislators in 26 states have introduced bills to crack down on parents who request vaccine exemptions for either personal or religious reasons. Three states — Washington, Maine and New York — have passed those measures. A fourth — California — is likely to pass its version next month.

The rush of legislation comes against the backdrop of the worst outbreak of the measles virus in more than a generation. In the first six months of the year, the Centers for Disease Control and Prevention reported 1,095 cases of measles across 28 states.

Read more at The Hill.