The U.S. Department of Justice has opened a probe into the $4.5 billion college licensing business, according to the industry's biggest player.

IMG's College Licensing Company (CLC) division said Wednesday it is "cooperating" with the DOJ inquiry. The DOJ declined to comment Wednesday night.

Cory Moss, senior vice president and managing director of CLC, said the feds have "opened a preliminary inquiry in how colleges and universities select which companies they license and how they determine their royalty rates."

The DOJ didn't tell them "much," said Moss. But CLC will "fully cooperate" with the investigation. "We're actually extremely eager to cooperate," he said.

Sales of licensed college t-shirts, sweatshirts, hats and other gear generate billions at retail outlets each year. The lucrative licensing business keeps growing.

IMG's CLC is the biggest player in the business, representing over 200 collegiate properties including Alabama, Auburn, Texas, Florida, Tennessee, Michigan and UCLA. CLC works with over 3,000 licensees nationwide that manufacture licensed college apparel, souvenirs and video games, according to Moss.

Moss said the federal probe could be related to a letter sent by a Washington, D.C., law firm to IMG College and 27 Football Bowl Subdivision schools this spring demanding they stop what the law firm alleged is a "concerted effort" to limit the number of manufacturers that are licensed to make collegiate apparel items.

Attorney Steven G. Bradbury of Dechert LLP declined to identify who his firm is representing. But in his five-page cease-and-desist letter on June 9, he wrote he represents "various stakeholders who share a common interest in preserving competition and choice in the supply of licensed collegiate merchandise."

Bradbury declined comment Wednesday night.