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Shelves at some grocery stores are sitting empty after an IT problem at a major food distributor.

United Natural Foods, or UNFI, said on Monday that “unauthorized activity” on some of its IT systems has “temporarily impacted the Company’s ability to fulfill and distribute customer orders.”

“The incident has caused, and is expected to continue to cause, temporary disruptions,” UNFI said in a filing with the Securities and Exchange Commission on Monday morning.

At some stores, that meant shelves appeared to go empty over the weekend.

One post late Sunday on a Reddit page dedicated to Whole Foods included photos showing largely bare cooler cases that normally contain yogurt, milk, and other dairy products. The poster did not immediately respond to a message from Business Insider.

“We are experiencing a temporary out of stock issue for some products,” a sign on one of the cooler doors read in the photos. “We apologize for the inconvenience and should have your favorite products back in stock soon.”

BI was unable to determine the scale of the outage. Whole Foods did not immediately respond to a request for comment. UNFI has a supply agreement with Whole Foods that lasts until 2032.

UNFI does not disclose all of the supermarket chains that it works with. The company says that it supplies about 30,000 individual stores “ranging from some of the largest grocers in the country to smaller independents.”

Do you have a story to share about the UNFI outage? Contact this reporter at abitter@businessinsider.com.