Dairy owner Mark McAfee started selling raw milk in 2000, marketing it to customers who believe it contains beneficial microbes that treat everything from asthma to autism.

The unpasteurized milk swiftly caught on as part of the growing natural food movement. But the Food and Drug Administration considers McAfee a snake oil salesman and recently launched an investigation into whether his dairy illegally shipped raw milk across state lines. The agency even tried to recruit one of his employees to secretly record conversations with him.

The case against McAfee is part of a crackdown on raw milk by government health officials who are concerned about the spread of food-borne illnesses. Lawmakers and law enforcement agencies are stepping up efforts to keep unpasteurized milk out of reach, even as demand for the niche product grows.

McAfee, who was among the first in California to sell raw milk on a large scale,brushed off the investigation: "When you're a pioneer, you have to expect to take a few arrows."

Twenty-two states prohibit sales of raw milk for human consumption, and the rest allow it within their borders. The FDA bans cross-border sales.

In Pennsylvania, local officials recently busted two dairies unlawfully selling milk straight from the cow.

And in Maryland, health officials issued an emergency ban late last year on "cow-sharing" agreements, claiming they were aimed at skirting a ban on raw milk sales.

"Raw milk should not be consumed by anyone for any reason," said John Sheehan, head of the FDA's dairy office. "It is an inherently dangerous product."

But shutting down sales is tricky because the federal government has largely let states regulate the raw milk industry. The result is a hodgepodge of laws that confuse consumers, dairy farmers and regulators alike.

McAfee said he expects the FDA's criminal probe to be dropped without charges in a deal that will require him to guarantee his interstate shipments are for use only as pet food. The FDA declined to comment.

Raw milk proponents insist they are under siege by state and federal regulators intent on snuffing out the industry.

The popularity of raw milk is fueled by consumers' concerns about the chemicals and hormones used in traditional dairy farming, and a growing interest in unprocessed, organic foods.

Devotees of raw milk ascribe to it almost mythical healing powers. They feed it to babies, believing it strengthens the immune system and staves off digestive troubles. The heat used in pasteurization, they say, kills healthy natural proteins and enzymes.

"It's a magic food," said Sally Fallon, president of the Weston A. Price Foundation, a nonprofit that advocates consumption of natural foods.

The FDA insists pasteurization destroys harmful bacteria without significantly changing milk's nutritional value. The process also extends its shelf life.

Nevertheless, some consumers have formed cooperatives to support dairy farmers who offer raw milk. They also join "cow-sharing" programs in which farmers take care of cows that are "leased" by consumers.