Digital marketer Mailchimp has removed several anti-vaccination activists from its platform and will no longer provide services to newsletters that push anti-vaccination content.

The move to block the anti-vaccination rhetoric follows similar actions by other tech companies and comes on the heels of increased pressure from public health advocates and lawmakers on digital platforms to curtail the spread of health misinformation.

“Mailchimp has shut down a number of accounts for anti-vaccination content that violates our Terms of Use, and we’re adding this category to our routine searches for prohibited content,” a Mailchimp spokesperson said in a statement provided to NBC News. “Spreading misinformation about the safety and efficacy of vaccines poses a serious threat to public health and causes real-world harm. We cannot allow these individuals and groups to use our Marketing Platform to spread harmful messages and expand their audiences.”

The company began quietly enforcing this decision last week.

“We trust the world’s leading health authorities, like the CDC, WHO, and the AAP, and follow their guidance when assessing this type of misuse of our platform,” the spokesperson said, referring to the Centers for Disease Control and Prevention, the World Health Organization and the American Academy of Pediatrics.

Vaccine misinformation that had once been allowed to flourish on the fringes of many mainstream internet destinations has come under growing scrutiny in the past six months, particularly as health officials have warned about the resurgence of some preventable diseases.

Earlier in 2019, Amazon pulled anti-vaccination documentaries from its Prime Video service and several books from its marketplace. Facebook began to stop advertising that spread “vaccine hoaxes” and said it planned to reduce the visibility of vaccine misinformation shared on its platform. YouTube also disabled advertising on anti-vaccination videos and lowered in ranking health misinformation content in its search results. Pinterest has blocked all vaccine-related search results.

These denials by the platforms have come as a shock to anti-vaccination advocates who for years were served well by recommendation algorithms that boosted controversial and conspiratorial content, such as the underlying and discredited notion that vaccines cause autism, a unifying theory for anti-vaccination groups.

The spread of such false information has increased vaccine hesitancy among parents, leading to the resurgence of vaccine-preventable diseases. This year, 1,022 measles cases have been confirmed in 28 states, the largest number of cases since 1992, according to the CDC. Seven states are currently experiencing an outbreak of measles, a disease that was officially eradicated in the United States in 2000.

Mailchimp, which has long been one of the most popular email marketing services, announced this week its expansion into original content creation with plans to roll out series, films and podcasts on topics surrounding entrepreneurship in 2019.

Since Mailchimp’s decision to ban anti-vaccination content, activists have been quietly scrambling to find new hosts for their email distribution lists, both the original method political and issue activists used to connect with volunteers and donors before the ubiquity of social media, and now one of the final frontiers to reach their audiences and solicit donations following the wider crackdown.

Anti-vaccine activist Larry Cook wrote about Mailchimp’s policy decision in a newsletter to followers Wednesday.

“If you have not yet heard, Mailchimp -- an email program I have used to send emails to subscribers for over four years -- has shut down numerous accounts because those accounts share "anti-vaccine" content,” Cook wrote. “As this war on our freedom has intensified and as censorship has increased, my expenses as an activist has also increased.”

Cook, who heads one of the most popular online anti-vaccination efforts and a Facebook group with more than 165,000 members, did not return a request for comment. In his newsletter, he told followers he hadn’t been booted from Mailchimp yet, but had already moved to Sendy, an alternative newsletter provider, as a precaution.

“This is not a matter of *if* you will get shut down, it's a matter of *when*” he wrote.