An investigation by the Federal Bureau of Investigation (FBI) into fraudulent media-buying practices has been confirmed by the Association of National Advertisers (ANA) in a letter to members about the possibility of cooperating with the agency.

Together with the U.S. Attorney’s Office for the Southern District of New York, the FBI is attempting to identify advertisers that may have been defrauded, ANA CEO Bob Liodice wrote in a letter to members. The FBI reached out to the industry organization’s outside counsel, and the ANA agreed to “share information about potential next steps member companies can take with the FBI if they believe they have been victimized.”

Suggestions included retaining legal counsel, reviewing media-buying history and contracts, and conducting audits for indications of fraud. Whether advertisers elect to help the feds is their own decision, the ANA said.

After characterizing the investigation as “a significant event to the industry and to ANA members,” Liodice wrote that “each member’s decision to cooperate with the FBI and federal law enforcement, or take any other action or no action is entirely voluntary and up to the member company.”

The Wall Street Journal first reported about the investigation in September, but the FBI declined to confirm its existence. Industry members pointed to a 2016 report from the ANA that highlighted nontransparent practices in the media-buying industry (such as cash rebates to media agencies) as the trigger for the federal probe.

Although the ANA letter provided confirmation of the FBI’s investigation, the organization emphasized its limited role.

“While we view the FBI’s investigation as important, the ANA itself cannot provide help to the FBI other than to share communication and information with our members,” according to the letter. “The ANA will not play a coordinating role on decisions or information between or among member companies and will not be a conduit between the FBI and member companies regarding individual company information. The FBI is aware of our communication with members and has requested we do so in order to obtain assistance.”

Why it matters: Details on the scope of the investigation are few, but the FBI’s request to have the ANA reach out to members demonstrates that the probe is ongoing and that member companies could be hearing from the feds soon.