In a move likely to draw a legal challenge, the state's elections agency voted unanimously Tuesday to require backers of thinly veiled campaign ads to disclose who pays for them.

The Government Accountability Board spent months deliberating whether it can and should regulate so-called "issue ads," which air during election season but don't explicitly urge the public to vote for or against a candidate.

On Tuesday the six retired judges who make up the board voted to subject the ads to regulation, the first step in a lengthy process to develop new rules requiring ad backers to register with the board, ban corporate money for the ads and disclose who funds the ads.

"They struck a very important blow for the public's right to know," Mike McCabe, executive director of the Wisconsin Democracy Campaign, said of the board's decision.

But R.J. Johnson, a spokesman for the Coalition for America's Families, which aired issue ads in this year's Assembly races, criticized the decision.

"We're seeing a very dangerous trend here where members of the judiciary and former members of the judiciary are basically creating law out of whole cloth," Johnson said. "It should worry defenders of the First Amendment everywhere."

A few days before the Nov. 4 vote, a Jackson County judge had ordered Johnson's group to stop airing one ad. But a state appeals panel later lifted the ban.

Mike Wittenwyler, a lawyer for the Coalition for America's Families and other groups that air issue ads, said the groups will likely sue the board after final rules are passed if they are similar to the rules adopted Tuesday.

"It's highly likely that whatever they do will be challenged because it will restrict what some organizations will be able to do," Wittenwyler said. "It will likely have to be a court challenge."

The board will have to hold a hearing on the rules, which could be modified. And the rules would be subject to legislative review. McCabe and Wittenwyler said it's possible the rules could be ready for implementation by the 2010 election.

The rules, prepared by campaign finance experts at the Brennan Center for Justice at the New York University School of Law, would govern ads that have "no reasonable interpretation other than as an appeal to vote for or against a specific candidate."

Those ads would be defined as appearing within 30 days of a primary election and 60 days of a general election and which:

• Refer to the "personal qualities, character or fitness" of a candidate.

• Support or condemn a candidate's position on issues.

• Support or condemn a candidate's public record.

McCabe said third-party groups paid for issue ads and other election material in two dozen Assembly districts in the weeks leading up to the Nov. 4 election. In 15 of those districts, the groups spent more money than the candidates, and in 10 the groups aired television ads.

In other action Tuesday, the Government Accountability Board:

• Directed agency staff to come up with recommendations for performing identity checks on all voters registered since January 2006. Such recommendations might tell clerks how to handle voters whose registration information does not match their name or address on their driver's licenses, among many other scenarios.

• Stood by its decision to no longer allow public officials to hold investments in blind trusts. The board made the decision last month, but lawyers for Attorney General J.B. Van Hollen and Supreme Court Justice Patience Roggensack said the rules would be unfair if applied to their clients.  

The Associated Press contributed to this report.