Twitter is announcing major limits on how users and apps can automate tweets, in order to combat spam and political propaganda bots. Developers are now banned from using any system that simultaneously posts “identical or substantially similar” tweets from multiple accounts at once, or makes actions like liking, retweeting, and following across multiple accounts at once. Twitter will remove these options from its own TweetDeck app, and third-party developers have until March 23rd to comply.

Twitter says these actions are “an important step in ensuring we stay ahead of malicious activity targeting the crucial conversations taking place on Twitter — including elections in the United States and around the world.” It alluded to the plan last month, when it revealed that over 50,000 accounts were linked to Russian propaganda efforts.

No “bulk, aggressive, or very high-volume automated retweeting”

The company laid out a series of specific policies and exceptions for account automation. Instead of sending the same tweet from multiple accounts, users can send one tweet and have multiple accounts retweet it, but they can’t use “bulk, aggressive, or very high-volume automated retweeting.” The ban on bulk tweeting applies regardless of whether you’re posting a bunch of duplicate tweets at once or scheduling them across a longer time period. Apps can still cross-post alerts from other services (like RSS readers) to Twitter, but only to a single account.

These new rules don’t apply to alerts for “weather, emergency, or other public service announcements of broad community interest” — so a tsunami warning, for instance, could be posted across a lot of different accounts at once.

Generally, though, Twitter offers two guiding rules. “Posting duplicative or substantially similar content, replies, or mentions over multiple accounts you control, or creating duplicate or substantially similar accounts, with or without the use of automation, is never allowed,” it says. Neither is posting multiple updates (from any number of accounts) to a trending topic “with an intent to subvert or manipulate the topic, or to artificially inflate the prominence of a hashtag or topic.” It’s a blanket rule that gives Twitter authority to shut down anything it sees as “inorganic” tampering.

Twitter is talking about these rules in terms of election propaganda. They coincide with what appears to be a significant attempt to purge bot accounts, which reportedly also temporarily locked some human users’ accounts. But the new rules are also a pretty substantive change to the platform — and they’ll have an effect on any app or company that cross-posts content to multiple accounts.