Two brothers were arrested Thursday on charges they fraudulently presented more than a half-dozen political action committees they controlled as advancing a host of causes, from supporting law enforcement to pro-choice advocacy, when in reality virtually none of the $23 million they raised since 2014 went towards political contributions, federal prosecutors claim.

William Tierney and Robert Tierney founded and directly operated six PACs, and oversaw the handling of at least three others, according to the U.S. Attorney's Office for the Southern District of New York. Over the past decade, the PACs raised more than $50 million from tens of thousands of donors. But for every dollar raised, U.S. Attorney Geoffrey Berman of the Southern District of New York said less than a cent actually went towards political efforts. The defendants, however, allegedly walked away with more than $3.5 million.

“As alleged, the defendants secretly operated numerous political action committees, raising small-dollar donations from people who believed their hard-earned money would support the causes described in solicitation calls and mailings,” Berman said in a statement. “In reality, as alleged, these PACs were political action committees in name only—they engaged in no advocacy campaigns, education efforts, or political operations, and donated less than 1 percent of the money they raised to candidates for office, all while personally enriching the defendants.”

Berman said the case is, as far as his office knows, the first prosecution of its kind to target “scam PACs,” calling them a growing problem “hiding in the tall grass of our political system.” He noted that in the 2016 election cycle, some 8,000 PACs received over $4 billion in funds, representing half of all the election spending.

“Media reporting suggests that this is not an isolated incident,” Berman said during a separate conference call with reporters. “Clearly the potential for abuse … is significant, and potentially widespread.”

Prosecutors allege the Tierneys went to lengths to mask their activities. Shell companies were created as pass-through entities. Donated funds were transferred to the accounts of these companies, which prosecutors claim were given names to make them seem related to marketing, consulting and communications efforts.

Even the telemarketers who worked the phones for the PACs were told to create shell companies to try and prevent the Federal Election Commission, donors and other members of the public from being able to follow the money, federal authorities claim.

According to the U.S. Attorney's Office, William Tierney is represented by Wiley Rein of counsel Robert Walker and partner Ralph Caccia. His brother, Robert, is said to have retained London & Mead name attorney Christopher Mead and attorney D. Bradley Clements. Neither set of attorneys responded to a request for comment.

The defendants were expected to be presented Thursday afternoon in the U.S. District Court for the District of Arizona.