FedEx and UPS are the targets of a federal criminal investigation related to their dealings with online pharmacies, which are at the center of an international crackdown on prescription drug abuse.

The shipping companies made the disclosures in regulatory filings over the last several weeks. A FedEx spokesman confirmed that the company is under investigation for allegedly aiding and abetting online pharmacies that illegally ship prescription drugs.

The investigation of the country's two largest shippers stems from a blitz against online pharmacies that was launched in 2005. Since then, dozens of arrests have been made, thousands of websites shut down and tens of millions of dollars in pills seized worldwide as investigators continue to broaden the probe beyond the operators.

Last year, Google Inc. agreed to pay $500 million to settle allegations by the Justice Department that it profited from ads for illegal online pharmacies.

A federal jury convicted three men of operating illegal pharmacies that used FedEx and UPS to deliver drugs without proper prescriptions. Seven others have also been convicted this year.

UPS said it was cooperating with the investigation and is "exploring the possibility of resolving this matter."

FedEx was more defiant. A company spokesman said the company has no plans to plea bargain with federal officials.