Schools across the country are having a problem providing milk for their students during breakfast and lunch meals. No, there’s no milk shortage. Instead, milk producers are having trouble acquiring the half-pint cardboard cartons that are a staple of school cafeterias. Here’s what you need to know about the milk carton shortage.

On October 25, the U.S. Department of Agriculture’s Food and Nutrition Service (FNS) posted a memo saying state agencies could allow program operators, which include schools, to serve meals with “an alternate form of fluid milk or without fluid milk” for the time being due to “milk supply chain challenges related to packaging issues.” This memo came in the wake of increasing reports of schools being unable to obtain milk for their cafeterias due to packaging supply chain problems.

That’s what everyone wants to know. As industry publication PackageDrive points out, some are citing issues at a company called Pactiv Evergreen, which bills itself as “the leading manufacturer of fresh food and beverage packaging in North America.” Milk provider Cream-O-Land recently posted a notice on its website saying that it may have to alter orders because its main carton supplier, Pactiv Evergreen, is “experiencing major production issues.” However, the problem causing the shortage is still a mystery. Earlier this year the company announced it expected to close one of its paper mills and one of its converting facilities, but it’s unknown if these closures are affecting the production of milk cartons.

Not much, at least not publicly. Cream-O-Land stated that “Pactiv Evergreen has notified us that it will supply less than 50% of our weekly needs of cartons to meet customer demand in the eastern United States” but it did not cite a reason why. Fast Company has reached out to Pactiv Evergreen for comment.

Cream-O-Land’s notice said that it tried to purchase cartons from a packaging company called Tetra Pak, which Cream-O-Land said was “the only other carton supplier in the United States” but Tetra Pak said it was no longer accepting new orders due to increasing demand from its existing customers. Fast Company has reached out to Tetra Pak for comment.

It’s likely every state in the country will feel the pinch from the milk carton shortage. School districts that have currently acknowledged it include those in the states of California, New York, Pennsylvania, and Washington.

The New York Times says that school districts in the above states could see the milk carton shortage last into early 2024.

Most school districts will still attempt to serve milk with meals, which is a law in many states. The Times reports that some school districts have said they will buy milk in bulk and manually pour it for the children and place a lid on the cups. Other districts have said they will provide self-serve milk stations that students can use.