In the aftermath of a presidential election campaign in which business and labor groups made millions in undisclosed campaign contributions, a group of retired Pennsylvania judges has taken the unusual step of calling on Congress to require donors to disclose who they are.

Business and labor unions spent record amounts following the Supreme Court's 2010 Citizens United decision, which overturned laws that limited campaign spending by special interests. The judges called on Congress to enact legislation that would require donors be identified.

"I would hope that both parties would understand that they are not hurt by disclosure," said retired Court of Common Pleas Court Judge Robert K. Young, of Emmaus. "It goes to credibility. If you have a million and want to spend it, spend it. But tell us who you are."

Young is joined in the effort by 10 other retired judges, including former federal district court Judge Edward Cahn, now a lawyer with the Philadelphia-based firm of Blank Rome L.L.P., and former Bucks County Orphans Court Judge Leonard Sokolove.

"This is a matter of doing the best that can be done in light of the fact that PACs [political action committees] can give billions for the benefit of a candidate or candidates," Sokolove, a resident of Newtown, said. "You have a sense of where the message is coming from. This principle applies to both sides."

Young said judges supporting the proposal were concerned voters weren't getting the full story about political advocacy when the sponsors of many advertisements are hidden from public view.

The group modeled its proposal on legislation introduced by Sen. Bob Menendez (D., N.J.) and other Senate Democrats last year requiring that all donors to so-called super PACs be disclosed through filings to the Federal Election Commission.

The long and tortured tale of federal campaign finance law reached a critical juncture in 2010 when the U.S. Supreme Court, in a 5-4 decision, ruled that the McCain Feingold Act banning contributions by corporations and labor unions to so-called independent expenditure groups violated the first amendment's free speech protections.

Before McCain-Feingold, named for primary sponsors Sen. John McCain (R., Ariz.) and former Sen. Russ Feingold, a Democrat of Wisconsin, these political action committees were permitted to spend special-interest money so long as they did not expressly advocate for or against a candidate. The Supreme Court decision overturned McCain-Feingold's ban on labor unions and corporations making such expenditures.

Current law requires that in certain instances donor identities be disclosed. But a loophole permits PACs to collect huge sums without disclosing the identity of donors from groups defined for tax purposes as social welfare organizations.

Those organizations are identified in Federal Election Commission records, but their contributors are not. Among such contributors in the last election were the liberal Priorities USA and Crossroads GPS, the super PAC of Republican election strategist Karl Rove.

Young said his interest in promoting changes to the disclosure rules stems from his long career on the bench. The background and interests of witnesses typically are central issues in both civil and criminal trials, he said, and such information is key to evaluating their credibility.

In the same way, he said, voters should have an opportunity to fully analyze arguments in political campaigns by knowing who is making them.