The U.S. Justice Department is investigating the Abbott Laboratories infant formula plant in Michigan that was shut down for months last year due to contamination, the company confirmed.

The factory’s closure in February 2022 was a key cause of a nationwide baby formula shortage that forced parents to seek formula from food banks, friends and doctor’s offices. Production restarted in June.

The Justice Department has informed Abbott of its investigation and the company is “cooperating fully,” Abbott spokesperson Scott Stoffel said via email. He declined to provide further details.

The investigation was first reported by The Wall Street Journal, which said the Justice Department’s consumer protection branch is looking into conduct at the Sturgis, Michigan, plant that led to its shutdown.

Abbott closed the factory after the Food and Drug Administration began investigating four bacterial infections among infants who consumed powdered formula from the plant. Inspectors uncovered several violations at the plant, including bacterial contamination, a leaky roof and lax safety protocols. But Abbott has stated that its products have not been directly linked to the infections, which involved different bacterial strains.