SAN FRANCISCO — Twitter said Monday that it was suspending Rep. Marjorie Taylor Greene from its service for 12 hours after she posted messages that violated its policy against sharing misleading information about the coronavirus.

Greene, R-Ga., has been an outspoken opponent of vaccines and masks as tools to curb the pandemic. In tweets Sunday and Monday, she argued that COVID-19 was not dangerous for people under the age of 65 who are not obese, 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 Greene’s home state, Georgia, new cases have increased 193% in the past two weeks.

Twitter said 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 spokesperson said. The company also added labels to Greene’s posts about the vaccines, calling them “misleading” and pointing to information about the safety of the inoculations.

In a statement, 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 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.

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 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.