A cyberattack on Rhode Island-based United Natural Foods Inc. (UNFI), one of the U.S.’s largest organic food distributor has led to empty shelves at Whole Foods stores across the country, reports NBC News. UNFI is a major partner with Whole Foods. It became aware of a cyberattack on June 5, according to a filing with the Securities and Exchange Commission, and took some of its systems offline, hampering its ability to distribute orders to customers.

NBC News said the attack comes in the wake of a series of cyberattacks where a notorious cybercriminal gang has been targeting major retail customers with ransomware, rendering key systems inoperable as hackers demand payment.

A UNFI spokesperson said there was not a clear timeline for when distribution would return to normal, but that on June 19 it had begun gradually bringing some systems back online.