Idaho election officials said it was unacceptable for a group to shield its financial backers from the public and renewed demands that it disclose its sources of money as required by the state's campaign finance laws.
Secretary of State Ben Ysursa's office on Monday reiterated its contention that Education Voters of Idaho is a political committee that must report contributors.
Education Voters of Idaho has chipped in more than $200,000 to pay for broadcast advertising in support of public schools chief Tom Luna's education overhaul ahead of the Nov. 6 vote.
But the group hasn't said where it got its money, instead maintaining it's a nonprofit whose supporters' identities enjoy federal protections.
In a statement on Monday, its founder, John Foster, said his group "won't back down" from Ysursa's challenge.