Short-sellers have been ramping up their bets against tether, the world’s largest stablecoin, amid a broad market selloff that has called into doubt the financial health of some crypto companies.

In the past month, more traditional hedge funds have executed trades to short tether through Genesis Global Trading, one of the largest crypto brokerages for professional investors. These trades are worth “hundreds of millions” of dollars in notional value, said Leon Marshall, Genesis’s head of institutional sales. He declined to be more specific.