Mark Zuckerberg's hearing has Facebook traders bracing for the worst

Facebook‘s stock has taken a serious beating in the weeks leading up to CEO Mark Zuckerberg’s planned appearance in front of Congress on Tuesday.

And based on how traders are positioning ahead of the 2:15 p.m. ET testimony, they think the selling can get even worse.

Short interest – or a measure of bets that a stock will decline – has spiked to 0.43% of shares outstanding for loan, its highest since September 2015, according to data compiled by IHS Markit. The gauge has more than doubled from its levels in mid-March.

The surge in short interest shows just how concerned investors have gotten in just a short amount of time. After all, many investors hold short positions as hedges, with hopes of protecting the money they’ve already made in a stock.

If these traders are able to cash in, that would mean Facebook’s shares added to their already-drastic 16% decline since the start of February. The firm’s issues have snowballed in earnest since reports first indicated that the political-research company Cambridge Analytica improperly accessed 50 million Facebook user profiles. Facebook later said that number was as high as 87 million.