Trent Arsenault of Fremont has fathered 14 children since he began donating sperm in 2006, the San Francisco Chronicle reported Monday.
However, the U.S. Food and Drug Administration told the man to stop giving away his sperm, or face charges.
The FDA said Arsenault is violating federal regulations that require blood tests every time a person donates any kind of body tissue or fluid.
"There's this thought process that they can use somebody they know and it's OK. But just because you 'know' someone, doesn't mean you 'know' them," said Dr. Mitch Rosen, director of the University of California, San Francisco Fertility Preservation Center. "You're taking a risk."
Arsenault said he has been tested at least five times over the past five years, but very few of his donations were given within the seven-day period required by law.
Arsenault contends he's being targeted by the FDA because he has a Web site that promotes himself and his willingness to donate his sperm.
"What the FDA is doing infringes on reproductive rights. The government is reaching into the bedroom," Arsenault said. "There's no precedence for my case. Whatever happens to me kind of sets the future up for all the other people in these situations -- the couples plus the donors."