A year ago, U.S. Food and Drug Administration officials sent a warning letter to Pennsylvania dairy farmer Daniel L. Alllgyer, saying they suspected he was illegally selling unpasteurized milk across state lines. He was told to stop.

A subsequent inspection of the farm revealed it was still “producing, packaging, selling, and distributing unpasteurized and unlabeled milk for human consumption in interstate commerce,” according to the federal food-safety agency.

On Tuesday, following another warning letter, the FDA announced it had requested a permanent injunction against Allgyer’s Rainbow Acres Farm in Kinzer, PA.

The agency is accusing Allgyer of selling raw milk in violation of the federal Public Health Service Act, which prohibits the interstate commerce of milk and milk products unless they are pasteurized. The complaint, filed April 19 in U.S. District Court for the Eastern District of Pennsylvania, also alleges that Allgyer is breaking the law by failing to label his milk as unpasteurized.

Since the government’s scrutiny of Allgyer’s dairy operations last year, the farm in Pennsylvania’s Amish Country has been championed by raw milk advocates who hope to overturn the federal ban on interstate raw milk sales.

More than half the states permit the sale or distribution of unpasteurized milk and there is no law against consuming raw milk. But interstate sales are illegal.

Because raw milk can contain a wide variety of harmful bacteria — including Listeria, E.coli, Salmonella, Campylobacter, Yersinia, and Brucella — FDA has long maintained a public health posture consistent with American Medical Association policy, which states that “all milk sold for human consumption should be required to be pasteurized.”

There have been no illnesses connected to milk produced at Rainbow Acres Farm, but elsewhere in Pennsylvania, where in-state sales of raw milk are legal from licensed, inspected dairies, unpasteurized milk has been the source of several outbreaks in recent years.

In 2010, 10 people who drank raw milk in Pennsylvania became infected with Campylobacter; one developed Guillain-Barre Syndrome, a condition that causes paralysis. In 2008, 65 people became ill with Campylobacter after drinking raw milk. In 2007, two outbreaks of Salmonella infections, which together sickened 42 people, were linked to the consumption of raw milk and cheese in Pennsylvania.

If the federal court grants an injunction against Rainbow Acres Farm, it would be prohibited from selling its unpasteurized milk in interstate commerce.