Twitter is down more than 5% Tuesday after Citron Research tweeted that it is the most vulnerable social media company to privacy regulation.

Social media stocks have been under pressure amid fears of more regulation after it was discovered last week that Cambridge Analytica accessed the data of 50 million Facebook users without their permission.

Twitter pushes back against Citron's claims.

Twitter shares are down more than 5% Tuesday after Citron Research tweeted it's the social media company "most vulnerable to privacy regulation." Twitter was down roughly 2.5% ahead of the tweet, and has since doubled its losses.

"Citron short $ TWTR," the firm tweeted Tuesday morning. "Near-Term target $25 Of all social media, they are most vulnerable to privacy regulation Wait until Senate finds out what Citron has published." The firm said in an accompanying note that it had sold its long position in Twitter, and is now taking a short position.

Citron's warning comes a little over a week after it was discovered that Cambridge Analytica accessed the data of 50 million Facebook users without their permission. That news sent social media stocks into a tailspin amid concerns of more government regulation.

Citron's note focused on what seems to reflect Twitter's particular vulnerability to privacy regulation; its dependence on data selling. "Twitter Will Generate $400 million this year by just selling user data," Citron said. "Not advertising."

Advertising revenue actually shrunk for 2017, while data licensing revenue grew. "In 2017, ad revenue declined to $2.11 billion from $2.25 billion in the prior year while data licensing revenue grew to $333 million from $282 million in the prior year," Citron said.

Furthermore, Citron points out company insiders have sold a large amount of Twitter stock. "Over the last year, insiders have sold/surrendered almost $300 million of stock," Citron added. "The last time there was this much insider selling was in 2015 when the stock was $50 and then preceded to fall to $14 over the next year."

A Twitter spokesperson said the company doesn't sell data pulled from direct messages.

"Twitter is public by its nature," the spokesperson said.

"Public Tweets are viewable and searchable by anyone. This is the power of Twitter. To be clear, our data licensing business does not sell DMs – any reports to the contrary are wrong. Our data licensing business helps capture the amazing uses of Twitter by building on that public data. Here's an example of one of the awesome uses from a few years ago."

Twitter shares are down 14% over the past week, but up almost 24% this year.