SAN FRANCISCO (AP) — Twitter, reacting to growing concern about misinformation spread on social media, is banning all political advertising from its service. Its move strikes a sharp contrast with Facebook, which continues to defend running paid political ads, even false ones, as a free speech priority.

“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,” Twitter CEO Jack Dorsey said Wednesday in a series of tweets announcing the new policy.

Facebook has taken fire since it reiterated in September that it will not fact-check ads by politicians or their campaigns, which could allow them to lie freely. CEO Mark Zuckerberg told Congress in October that politicians have the right to free speech on Facebook.

Zuckerberg wasted no time responding to Twitter’s move. During Facebook’s conference call for earnings, which began less than an hour after Dorsey’s tweet, the Facebook chief offered an impassioned monologue about what he called his company’s deep belief “that political speech is important.”

Zuckerberg stood by the company’s decision to run unchecked political ads and denied that the choice is financially motivated, saying such ads make up less than half of a percent of Facebook revenue.

Google did not have an immediate comment on Twitter’s policy change.

Trump’s campaign manager called Twitter’s change a “very dumb decision” in a statement Wednesday.

“This is yet another attempt to silence conservatives, since Twitter knows President Trump has the most sophisticated online program ever,” campaign manager Brad Parscale said.

The presidential campaign for former Vice President Joe Biden said it was “unfortunate” that companies would think the only option was to completely ban political ads.

“When faced with a choice between ad dollars and the integrity of our democracy, it is encouraging that, for once, revenue did not win out,” Bill Russo, the deputy communications director for Biden’s campaign, said in a statement.

Twitter’s policy will start on Nov. 22.