An American food producer that counts Butterball turkeys among its brands has done millions of dollars of business in Africa with a company blacklisted by U.S. authorities for supporting terror, The Wall Street Journal has found.

The Justice Department, as part of a broad criminal probe, is investigating whether Kansas-based Seaboard Corp. tried to mask wheat-flour sales to firms linked to a Lebanese businessman and his family in the years after he and two brothers were put on the government’s terror blacklist in 2009 and 2010.

The brothers have allegedly given tens of millions of dollars to Hezbollah, the Shiite militant group backed by Iran, U.S. officials said. Penalties for companies working with anyone on the list range from fines to prison under laws intended to starve terror groups of cash to carry out attacks.

U.S. multinational companies are responsible for seeing past middlemen, corporate shells and newly formed firms to spot links with more than 1,000 individuals, companies and entities named on the government’s designated-terrorist list. Prosecutions are rare, but companies risk civil penalties for even unintentional work.

“Doing business with bad actors is like touching the third rail,” said Christopher Swift, a lawyer who helped enforce sanctions against blacklisted terrorists at the Treasury Department before entering private practice. “If you deliberately do it, then that falls into the criminal domain—and that’s very dangerous.”