According to data from Datasembly, the ongoing baby formula shortage got worse throughout the month of April. After hovering between 2% and 8% in the first half of 2021, the out-of-stock rate of baby formula jumped to 23% in January, 29% in March, 31% in mid-April, and up to 40% by Apr. 24.

“Inflation, supply chain shortages, and product recalls have brought an unprecedented amount of volatility for baby formula,” Datasembly founder and CEO Ben Reich said in a statement last month. “We expect to continue to see the baby formula category being dramatically affected by these conditions.”

The shortages were prompted in part by the shutdown of a key production facility in Michigan this year. The plant, owned by Abbott Nutrition, has been the subject of an FDA investigation following reports of contaminated formula that was linked to the deaths of at least two infants.

“The formula shortage is a national crisis, hitting poor moms and kids the hardest,” Sen. Tom Cotton (R-AR) tweeted Monday. “The FDA needs to immediately step up, be transparent, explain how it will get production restarted, and give parents a timeline.”

According to The Hill, several major retailers have decided to ration purchases of baby formula amid the shortage. Target confirmed to The Hill it is limiting the sale of baby formula products, including some limits on the company’s website. Costco’s website also showed that members were limited to five baby formula units per member while supplies last. Meanwhile, CVS similarly said it would limit baby formula sales to three units per purchase, both in stores and online.

“Due to increased demand and various supplier challenges, infant and toddler formulas are seeing constraint across the country,” a Walgreens spokesperson told The Hill. “Similar to other retailers, we put into effect purchase limits of three per transaction on all infant and toddler formula to help improve inventory.”

CNN and CNBC contributed to this report.