Sources tell Local 4 the FBI on Tuesday raided the Detroit Public Library's main branch on Woodward.
Sources said six agents confiscated records.
No patrons were in the library at the time of the raid because it hadn't opened yet.
The Detroit library, like other arms of city government, has suffered financial problems. In 2011, there was a plan to close 18 of 23 branches. The plan was dropped after officials took a new look at revenue projections and figured in the savings from a smaller staff.
Two branches were closed, and 80 of 364 employees were dismissed. Most of the library's budget comes from a property tax.
Detroit Library Commission President, Jonathan Kinloch, said the action by the FBI is justified.
"Based on all of the concerns that have been raised over the past few months, you would expect that at this particular point there would be some outside review of the activities to see whether or not there's any wrongdoing," he said.