The US Food and Drug Administration (FDA) has warned Teva Pharmaceutical Industries over manufacturing violations at its California plant.
A letter release on Tuesday confirmed that a July 2009 inspection found problems with the manufacture of the sedative propofol at a Teva plant in Irvine, California.
Teva is accused of failing to test each lot of raw materials used to make propofol for toxins.
A letter raising FDA concerns was delivered to Teva in December 2009 but the regulatory authority deemed the company's response to be unsatisfactory.
The FDA's inspection coincided with the recall of 57,000 vials of propofol, after elevated levels of toxins were found in some lots.
A Teva spokeswoman said that the company was working with the FDA to address these concerns and has already re-scheduled a plant enhancement project from December to April.
Propofol is an injectable drug widely for general anaesthesia and sedation in operating rooms and intensive-care units, and was also implicated in the death of pop star Michael Jackson last year.