Wisconsin prosecutors have selectively targeted conservative groups to effectively chill their speech, lawyers for a conservative activist detailed in a Tuesday filing with a federal appeals court.

Eric O'Keefe, director of the limited government advocacy group the Wisconsin Club for Growth, in February sued prosecutors over a secret investigation into potential campaign finance violations by conservative groups during recall elections.

Two judges have already rejected the legal theory offered by prosecutors and the probe has been halted, but prosecutors have asked the U.S. Court of Appeals for the 7th Circuit to reopen the case.

Though the case has not produced evidence of actual violations of the law, it has been used by Democrats to suggest that the cloud of scandal hangs over Gov. Scott Walker, R-Wis., during his re-election bid.

At the center of the story is what’s known as a "John Doe" investigation, which, under Wisconsin law, allows prosecutors to conduct a probe in secret without naming their targets or publicly disclosing what the investigation is about.

The office of Milwaukee County District Attorney John Chisholm, a Democrat, launched two such investigations against allies of Walker. The one at issue in this case started in August 2012. During the investigation, prosecutors sent out subpoenas to dozens of conservative groups and used invasive tactics to gather information.

On Oct. 3, 2013, early in the morning, "armed officers raided the homes" of officials from the Wisconsin Club for Growth and other targets throughout the state, according to a court ruling this May. "Sheriff deputy vehicles used bright floodlights to illuminate the targets' homes," the ruling explained. "Deputies executed the search warrants, seizing business papers, computer equipment, phones, and other devices, while their targets were restrained under police supervision and denied the ability to contact their attorneys."

On Jan. 10, 2014, Judge Gregory Peterson, looking at the evidence, quashed the subpoenas and rejected the legal theory offered by the prosecutors. U.S. District Court Judge Rudolph Randa, nominated by President George H.W. Bush, also sided with Wisconsin Club for Growth in a decision halting the probe.

Arguing before the appeals court, lawyers for O’Keefe argue that the Wisconsin Club for Growth only ran issue ads, rather than ads expressly advocating for a candidate, and that there is no evidence that expenditures were coordinated with the Walker campaign.

Though the overzealous prosecution has not produced evidence of legal wrongdoing, it has had immediate ramifications for O’Keefe’s ability to exercise his constitutional rights, creating, in the words of the legal brief, an “ongoing and unmitigated chilling of Plaintiffs’ speech.”

O’Keefe’s lawyers explain that, “Plaintiffs’ First Amendment injury was immediate. O’Keefe’s associates began cancelling meetings with him and declining to take his calls, reasonably fearful that merely associating with him could make them targets of the investigation. O’Keefe was forced to abandon fundraising for the Club because he could no longer guarantee to donors that their identities would remain confidential, could not (due to the Secrecy Order) explain to potential donors the nature of the investigation, could not assuage donors’ fears that they might become targets themselves, and could not assure donors that their money would go to fund advocacy rather than legal expenses.”

The brief also argues that prosecutors have not sought to target liberal groups with the same ferocity under the same legal theory being employed by prosecutors against conservative groups.

Read the full brief below.

Merits Brief 1822 and Consolidated Cases