SAN FRANCISCO — Twitter said on Monday that it was suspending Representative Marjorie Taylor Greene from its service for 12 hours after she posted messages that violated its policy against sharing misleading information about the coronavirus.
Ms. Greene, Republican of Georgia, has been an outspoken opponent of vaccines and masks as tools to curb the pandemic. In tweets on Sunday and Monday, she argued that Covid-19 was not dangerous for people unless they were obese or over age 65, and said vaccines should not be required.
But cases of the coronavirus are on the rise, and the highly contagious Delta variant accounts for more than half of new infections in the United States, federal health officials said this month. In Ms. Greene’s home state, Georgia, new cases have increased 193 percent in the past two weeks.
Twitter said Ms. Greene’s tweets were misinformation, and it barred her from the service until Tuesday. “We took enforcement action on the account @mtgreenee for violations of the Twitter Rules, specifically the Covid-19 misleading information policy,” a Twitter spokesman said. The company also added labels to Ms. Greene’s posts about the vaccines, calling them “misleading” and pointing to information about the safety of the inoculations.
In a statement, Ms. Greene said Silicon Valley companies were working with the White House to attack free speech. “These Big Tech companies are doing the bidding of the Biden regime to restrict our voices and prevent the spread of any message that isn’t state-approved,” she said.
Twitter took action after President Biden called on social media companies to do more to combat the spread of vaccine misinformation on their platforms. On Friday, Mr. Biden said that sites like Facebook were “killing people” by allowing misinformation to flourish unchallenged, adding, “Look, the only pandemic we have is among the unvaccinated, and that — and they’re killing people.”
His statement capped weeks of frustration at the White House over the spread of online misinformation, which has led to vaccine hesitancy, health officials say.
Facebook, which took the brunt of the criticism, argued that Mr. Biden’s statement was unfounded. “The Biden administration has chosen to blame a handful of American social media companies,” Guy Rosen, Facebook’s vice president for integrity, said in a blog post on Saturday. “The fact is that vaccine acceptance among Facebook users in the U.S. has increased.”
On Monday, the president softened his criticism, saying that particular users were responsible for the spread of misinformation rather than Facebook. The company should do more to combat “the outrageous misinformation” spreading on its platform rather than taking his remarks as a personal insult, Mr. Biden added.
Twitter has long banned users from sharing misinformation about the coronavirus that could lead to harm. In March, the company introduced a policy that explained the penalties for sharing lies about the virus and vaccines.
“We’ve observed the emergence of persistent conspiracy theories, alarmist rhetoric unfounded in research or credible reporting, and a wide range of unsubstantiated rumors, which left uncontextualized can prevent the public from making informed decisions regarding their health, and puts individuals, families and communities at risk,” the company said in its policy against sharing Covid misinformation.
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People who violate that policy are subject to escalating punishments known as strikes and could face a permanent ban if they repeatedly share misinformation about the virus. A 12-hour ban, like the one Ms. Greene is experiencing, is Twitter’s response to users who have either two or three strikes. After four strikes, Twitter suspends users for seven days, and after five strikes, Twitter bars the user altogether.
Other Republicans who have been suspended from Twitter have complained that the social media company is censoring them.
In January, Twitter barred President Donald J. Trump after the company determined that his social media posts played a role in inciting violence during the riot at the U.S. Capitol. Mr. Trump has argued that Twitter and Facebook, which also suspended his account, were censoring him and said the companies required government oversight.
Ms. Greene was previously suspended from Twitter in April, but the company said it was a mistake caused by one of its automated systems for detecting spam and abuse.
“Everyone knows that’s a LIE, and it was no mistake,” Ms. Greene tweeted after her suspension was lifted.