The Wisconsin Club for Growth on Wednesday asked U.S. District Judge Rudolph Randa for the additional time. The conservative group is working with prosecutors and two unnamed parties to reach a deal on what documents to release.
Randa on July 2 granted an extension until Thursday for the parties to come to an agreement.
But Wisconsin Club for Growth says that timeline is "infeasible" due to the work required to review the 3,000 pages of documents in question.
No one has been charged in the probe which Randa put on hold in May.