Twitter’s stock price fell 11% to close at $29.29 Thursday after an investor note declared the company “toxic” and called it “the Harvey Weinstein of social media.” The note came in the wake of a recent Amnesty International report condemning harassment on the site.

The investment firm, Citron Research, is led by Andrew Left, who had announced in March that he had a short position in Twitter’s stock, CNBC reports. It’s not mentioned in the report if he still has that position.

“Citron has been following Twitter for years and when we read the just published piece from Amnesty International, we immediately knew the stock had become uninvestable and advertisers will soon be forced to take a hard look at all sponsorships with Twitter,” according to the report, which sets a price target of $20 for Twitter stock.

Based on Amnesty International’s estimates, a group of 778 women politicians and journalists in the U.S. and U.K. received “abusive or problematic tweets” once every 30 seconds on average during 2017. Women of color, especially black women, received more such tweets than white women, according to the study.

Citron contends that brands won’t want to advertise on a site known for harassment, but predicts that efforts to regulate speech on the site would drive users away.

“Ask anyone from Laura Ingraham to Kevin Hart to Tucker Carlson about how enthusiastic advertisers are about associating with anything that hints of intolerance,” says the Citron report.

At the time the Amnesty report came out, Twitter’s trust and safety lead, Vijaya Gadde, said the company is committed to improving discourse on the site.