Twitter on Wednesday said it would ban all advertisements about political candidates, elections and hot-button policy issues such as abortion and immigration, a significant shift that comes in response to growing concerns that politicians are seizing on the vast reach of social media to deceive voters ahead of the 2020 election.

Twitter CEO Jack Dorsey announced the shift in policy in a series of tweets, stressing that paying for political speech has the effect of “forcing highly optimized and targeted political messages on people.” The move marks a break with Twitter’s social-media peers, Facebook and Google-owned YouTube, which have defended their policies around political ads in recent weeks.

“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 said.

Twitter’s revised policy covers ads intended to influence elections including ballot measures, as well as those that address “issues of national importance." The new rules will be applied globally, and they are slated to take effect in late November.

But the change doesn’t affect what users on their own can tweet and share, meaning it may not have much impact on widely followed accounts, including President Trump’s, whose tweets already reach more than 66 million users each day. Some critics, including Democrats, have urged Twitter to block or remove the commander-in-chief’s tweets, arguing his comments are incendiary or incorrect. Twitter has declined to take action, beyond stressing some narrow cases in which it would limit the reach of tweets from a head of state.

Twitter’s decision also comes at a moment when one of Dorsey’s peers, Facebook CEO Mark Zuckerberg, continues to stand by a controversial policy that essentially allows politicians to lie in ads.

The issue first arose earlier this month, when former Vice President Joe Biden, who is seeking the Democratic nomination for the White House, asked Facebook to remove an ad from President Trump’s campaign that contained multiple falsehoods. Facebook declined, prompting backlash from other 2020 contenders. In response, Zuckerberg has defended the policy in recent weeks, stressing the tech giant should not stand in the wayof political leaders’ speech.

Political advertising long has proven a thorny issue for Silicon Valley. During the 2016 election, agents tied to the Russian government purchased promoted tweets and other forms of online ads as part of their campaign to stoke political discord, promote then-candidate Trump and undermine Democratic contender Hillary Clinton.

Regulators lambasted social-media sites for failing to spot such efforts by a foreign power to interfere in U.S. elections, and the pressure promoted major changes — including efforts by Twitter and others to more clearly label political ads, verify the individuals purchasing them and cache them for the public to view. Still, lawmakers threatened regulation, arguing that online ads were subject to far fewer, less restrictive rules than broadcast television.

In his tweets, Dorsey endorsed those calls for new federal laws.

“Ad transparency requirements are progress, but not enough,” he said. “The internet provides entirely new capabilities, and regulators need to think past the present day to ensure a level playing field.”