Two organizations known for anonymous spending, or "dark money," on political campaigns filed suit Thursday night to keep Arizonans from voting on a measure that would make the practice illegal. 

The executive director of the Free Enterprise Club and the state director of Americans for Prosperity filed the suit, which argues some of the paid circulators for the “Stop Dirty Money” campaign did not register with the Arizona Secretary of State's Office as required by law.

Attorney Kory Langhofer also claimed there were other violations, including that some circulators were convicted felons, which means their civil rights had not been restored and thus, ineligible to gather signatures.

Both groups say they don’t have to disclose their donors because under the federal tax code, both are considered “social welfare organizations.” The initiative proposes to put what amounts to “right-to-know” language into the Arizona Constitution.