The Supreme Court won't hear an appeal from a conservative group seeking to end an investigation into possible illegal coordination between Wisconsin Gov. Scott Walker's 2012 recall campaign and independent groups.

The justices on Monday let stand an appeals court ruling that said Wisconsin Club for Growth and its director, Eric O'Keefe, must resolve their claims in state courts.

No one has been charged as a result of the investigation which has sought documents and testimony about possible violation of state campaign finance laws.

The investigation is on hold while a separate legal challenge is pending before the Wisconsin Supreme Court.

The club and O'Keefe argued that the investigation was a violation of their First Amendment rights and an attempt to criminalize political speech.