Mexico City ? The U.S. Treasury Department on Thursday banned Americans from doing business with six Mexican companies and 12 people it said were fronts for a cartel run by a powerful drug kingpin.

It said the six companies – including a dairy and day care center – and individuals were involved in the operations of Ismael Zambada Garcia, identified as “one of Mexico’s most powerful drug kingpins,” who is based in the northwestern state of Sinaloa, home to many of Mexico’s top drug smugglers.

“The Zambada Garcia organization cannot hide behind front companies like the Sinaloa cattle and dairy business,” Drug Enforcement Administration Administrator Karen P. Tandy said in the news release.

She said her agency was working with the Treasury Department “to expose these traffickers’ front companies for what they really are: not legitimate businesses, but illegal cash cows that fuel the drug trade, its violence and corruption.”

The department’s designation under the so-called Kingpin Act freezes any assets they may have in the U.S. and prohibits anyone in the United States from doing business with them.

The law is meant to expose the networks traffickers use to hide and launder drug money and “cuts them off from the U.S. financial system,” according to the Treasury Department statement.

The director of one of the institutions listed, the Nino Feliz day care center in Culiacan, said her operation was “in no way” related to Zambada.

Carmen Olivia, interviewed by telephone, said the center, serving 240 children of working mothers, was privately owned but was financed by the federal Social Security service. “You can’t call it a big business. It’s more of a humanitarian thing,” she said.

Rodrigo Brand, a spokesman for Mexico’s Treasury Department, said it would feed information on the companies to Mexico’s federal Attorney General’s Office, which had no immediate comment on the announcement.

Among the individuals the Treasury Department identified as fronts were Zambada’s former wife, Rosario Niebla Cardoza, and their four daughters.

The State Department has offered a $5 million reward for information leading to Zambada’s arrest.

He was indicted in January 2003 on charges of smuggling $50 million worth of narcotics, mostly cocaine, into various American cities. Later that year, authorities said that Zambada’s organization had been the target of a 19-month binational investigation dubbed “Operation Trifecta,” which resulted in more than 240 arrests.