The secret John Doe probe is exploring possible illegal links between Gov. Walker's campaign and several conservative funders.
Late Thursday, Wisconsin's District IV Court of Appeals rejected several challenges to the continuing investigation. Prosecutors reportedly launched it a few months after Walker's 2012 recall election.
The court has ordered the release of some records related to the probe, but none identifying the parties under investigation or specific information that search warrants or subpoenas have been seeking.
Attorneys for the unnamed parties seeking to halt the John Doe argued that prosecutors illegally consolidated secret investigations underway in five counties - Dane, Dodge, Iowa, Columbia and Milwaukee. The appeals judges concluded that there is overlap because "targets may have interacted with other targets in different counties" so the same judge and special prosecutor can be involved in all of them.
The district court also refused to send the case to the Wisconsin Supreme Court, as the petitioners asked.
Thursday's ruling noted that Wisconsin Attorney General J.B. Van Hollen declined to conduct a multi-jurisdictional investigation, after prosecutors approached his office.