"Follow, unfollow, follow, unfollow. Who does that? Spammers. So we're changing the number of accounts you can follow each day from 1,000 to 400. Don't worry, you'll be just fine," the company tweeted late Monday.
Twitter last year cracked down on "bulk tweeting" that allowed accounts to tweet the same content from multiple accounts.
"As a part of our commitment to building a healthy service, we remain focused on stopping spam and abuse on Twitter," a spokesperson for Twitter told Engadget.
Last November, Twitter said it was giving users more freedom to report fake, suspicious accounts to intensify crackdown on online spamming activities.
You can now specify what type of spam you are seeing when you report, including fake accounts.
Twitter allows users to flag tweets as originating from a fake account or a bot which are impersonating as something or someone else, and mark them as "fake".
The company purged about 70 million accounts last year for conducting spamming or malicious behaviour.