Shipping companies FedEx and UPS say they are targets of a federal investigation related to their dealings with online pharmacies, ABC News reports. The probe is part of an international effort to reduce prescription drug abuse.

On Thursday, a federal jury convicted three men of operating illegal pharmacies that used the two shipping companies to deliver drugs without proper prescriptions, according to the news report.

FedEx spokesman Patrick Fitzgerald said the Drug Enforcement Administration has refused to provide the company with a list of online pharmacies under investigation. Without such information, it is not possible to know which companies are operating illegally, he told ABC News. “We have no interest in violating the privacy of our customers by opening and inspecting their packages in an attempt to determine the legality of the contents,” he said.

In 2011, Google agreed to pay $500 million to avoid being prosecuted for aiding illegal online pharmaceutical sales. In the settlement, the company acknowledged it had improperly and knowingly assisted online pharmacy advertisers, allegedly based in Canada, to run ads for illegal pharmacy sales that targeted American customers.