Twitter flagged one of President Donald Trump’s tweets on Monday, placing it behind a notice that warns users it violates the platform’s rules against dissuading people from voting.

In the tweet, posted on Monday, Trump claimed mail drop boxes are a “voter security disaster” and also said they are “not COVID sanitized.” Twitter’s notice says that the tweet violates its rules about civic and election integrity, but it “determined it may be in the public’s interest for the Tweet to remain accessible.” Users can still retweet it with comment, but are nor prevented from liking, replying, or retweeting it alone.

Through its Twitter Safety account, the company gave more details, saying that the tweet had been flagged for “making misleading health claims that could potentially dissuade people from participation in voting.” It also cited a section from its Civic Integrity Policy, highlighting a line that forbids users from making “misleading claims about process procedures or techniques which could dissuade people from participating” in elections.

Per our policies, this Tweet will remain on the service given its relevance to ongoing public conversation. Engagements with the Tweet will be limited.

Mail-in ballots, which are expected to be used more widely by states in response to the COVID-19 pandemic, have become a partisan issue leading up to the November presidential election. Despite what Trump said in his tweet, expert consensus is that mail-in ballots and absentee ballots are both secure. Furthermore, the Centers for Disease Control and Prevention states COVID-19 is spread mostly through close contact from person to person. Though it is possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their mouth, nose, or possibly eyes, the CDC says this is “not thought to be main way the virus spreads.”

After years of controversy over how the platform handled the president’s tweets that contained misleading, false, or incendiary statements, Twitter has recently begun taking a harder stance on Trump’s account. In May, Twitter applied fact-check labels about mail-in ballots to two of Trump’s tweets.

Days later, Trump signed an executive order targeting Section 230 of the Communications Decency Act, which gives internet companies legal protections that shield them from liability for user-created content while also giving them power to make moderation decisions. The executive order argued that platforms forfeit their rights to legal protection when they moderate content, as Twitter did when it applied fact-check labels to Trump’s tweets.