Pharmacy chains CVS Health Corp. and Walgreens Boots Alliance Inc. limited purchase of children’s pain drugs as they face supply constraints and high demand with the United States experiencing one of the worst flu season in a decade.

CVS said there is currently a two-product limit on all children’s pain-relief products at all its pharmacy locations and online, while Walgreens said it had put a limit of six over-the-counter pediatric fever reducers per online transaction.

Bloomberg Law, which first reported about the purchase limit, said U.S. supermarket chain Kroger Co. was also putting a limit over the purchases to two children’s pain medicine products.

Kroger did not immediately respond to a Reuters request for comment.