Billy Hunter's five-year, $15 million contract extension in 2010 as executive director was never approved by player representatives.
The possible violation of the NBPA's constitution raises questions about the legitimacy of Hunter's contract and his future as executive director.
The contract of union general counsel Gary Hall was never approved either.
As part of an ongoing probe, the law firm of Paul, Weiss, Rifkind, Wharton and Garrison has investigated the the business practices of the union under Hunter's leadership.
"NBPA should consider whether Hunter should remain as Executive Director," according to the report. "Hunter was aware that his current contract was never properly approved and...he knowingly failed to disclose this information."