Twitter announced Wednesday that it will no longer take political ads, a major step as tech companies work to deal with misinformation ahead of the 2020 election.

The ban will go into place in November.

In a series of tweets, Twitter CEO Jack Dorsey laid out the company’s reasoning, focusing on the downside of political advertising when combined with digital advertising.

“While internet advertising is incredibly powerful and very effective for commercial advertisers, that power brings significant risks to politics, where it can be used to influence votes to affect the lives of millions,” Dorsey tweeted.

“Internet political ads present entirely new challenges to civic discourse: machine learning-based optimization of messaging and micro-targeting, unchecked misleading information, and deep fakes. All at increasing velocity, sophistication, and overwhelming scale,” Dorsey added.

As tech companies have moved to counter the spread of fake news and misinformation after the 2016 election, they have been forced to make choices about whether legitimate political actors should be given extra leeway. In June, Twitter said it would label but not delete tweets from politicians who violated its rules.

Twitter’s decision puts it apart from other tech companies that have resisted calls to stop taking political ads. Critics site the powerful micro-targeting capabilities of tech platforms — which allow ads to be tailored to niche audiences and interest groups — as being susceptible to abuse, particularly when spreading false or misleading claims.

Facebook is currently embroiled in a debate over its decision to allow political campaigns to push ads containing misinformation. The company has said it does not think it should be the arbiter of political speech, though it does stop companies and political committees from using false information in ads.

Politicians, consumer watchdog groups and even some Facebook employees have called on the company to reconsider its stance.

Dorsey touched on the conflict between hosting paid political ads and trying to fight the spread of misinformation.

“For instance, it‘s not credible for us to say: ‘We’re working hard to stop people from gaming our systems to spread misleading info, buuut if someone pays us to target and force people to see their political ad…well…they can say whatever they want!'” Dorsey tweeted.

Dorsey also offered some details on the company’s thought process, noting that it considered only eliminating ads from candidates but felt that left open loopholes for issue-based ads.

Dorsey did not clarify how the company would determine what constituted a political or issue ad, but said the full policy would be published on Nov. 15 and include some exceptions, such as ads in support of voter registration. The policy will go into effect on Nov. 22.

Dorsey’s announcement appeared to directly address concerns from conservative activist groups that limiting the purchase of targeted political ads on social networks amounts to censorship or a restriction on free speech.

“This isn’t about free expression. This is about paying for reach. And paying to increase the reach of political speech has significant ramifications that today’s democratic infrastructure may not be prepared to handle. It’s worth stepping back in order to address.”

Renée DiResta, a Mozilla Fellow in Media, Misinformation and Trust, called Twitter’s new policy “recognition that their role as an amplifier carries responsibility.”

“This is paid speech,” she said. “You are not being deprived of free expression if a company doesn’t want to accept money to allow you to promote your speech. This is not being decided in a partisan matter.”

The details of Twitter’s policy will be closely watched in politics as well as in the tech industry, particularly for how it decides to draw the line on what is or isn’t a political ad. Will Oremus, a journalist for Medium’s tech-focused publication OneZeo, tweeted the question: How does Twitter decide what constitutes an issue ad?”

In response, Instagram head Adam Mosseri, who has been a vocal defender of Facebook’s policy, added: “That’s my first question as well.”