Mobileye shares plunged by more than 7% to below $40 per share during regular trading hours after Citron Research – a firm notorious for its often inflammatory short reports – called them the “short of the year” for 2016 in a tweet.

Citron reiterates its short recommendation on Mobileye

Here’s the tweet which lit the fire that’s burning down Mobileye shares as of this writing:

As is usually the case with any strong call on any stock, naysayers filled up Citron’s Twitter feed with opposing comments and reminders of the firm’s past mistakes, like its previous view on Netflix, which has skyrocketed.

Of course one thing MBLY investors should be worried about is whether the company loses Tesla Motors as a customer. Recently an email from Tesla CEO Elon Musk suggested that they might consider dumping Mobileye, which would be disastrous to the business. A Seeking Alpha post cites Bloomberg’s reference of an email Musk sent to software engineer George Hotz offering him a job at Tesla.

“I’m happy to work out a multimillion-dollar bonus with a longer time horizon that pays out as soon as we discontinue Mobileye,” the email read.

Mobileye short

Citron targeted Mobileye in September

Today’s tweet isn’t the first time Citron Research recommended shorting Mobileye. The firm issued a full report in early September in which it claimed that there’s “NOTHING in the past or present financials, business performance or realistic future technology prospects of Mobileye that would get it within miles of justifying its current $12 billion market cap.”

Citron noted that MBLY management has been selling off their shares right and left and set a price target of $25 per share, calling the company a “‘Hail-Mary’ bet on a blue-sky future that just does not exist.”

Mobileye compared to Volkswagen

Toward the end of September, Citron again called out MBLY as a strong short position after trimming their target to $20 per share based on the emissions scandal involving Volkswagen. The German automaker was accused of and admitted to using software that made some of its vehicles appear to give off lower emissions levels than they actually did. Citron claimed that the emissions scandal proves its analysis of MBLY, which the firm said sells its products to Tier 1 suppliers that are also its competitors.

“The Volkswagen debacle kills the theory that Mobileye can sustain monopoly-level margins and massive growth at the same time,” the firm wrote. “… This industry is ALL about saving money wherever it is possible and looking for every angle every year, every day.”