In a bid to limit the impact of “secret money” in the 2012 elections, a coalition of liberal-leaning groups announced a campaign this week aimed at pressuring corporations to reveal donations to political groups.

There is one complication, however: Many of the groups behind the effort also don’t disclose their donors to the public.

Most of the organizations behind the latest disclosure push — including Americans United for Change, Common Cause and Public Citizen — fall under a portion of the tax code that allows them to keep their donor details private. Some of the groups do reveal their biggest contributors voluntarily, but not at the level of detail required for political campaigns, super PACs and other explicitly election-oriented organizations.

The contrast underscores the muddiness surrounding much of the disclosure debate, because a broad array of the nonprofit groups that advocate for greater transparency in political donations are often not required to make such disclosures themselves.

Crossroads GPS, a nonprofit conservative group that has come under regular fire from liberal organizations for not disclosing its funders, accused its rivals of hypocrisy for seeking refuge under the same confidentiality laws that they criticize.

“They don’t disclose their donors, nobody knows who gives them money,” said Jonathan Collegio, a spokesman for Crossroads GPS and its affiliated super PAC, American Crossroads. “But here they are, trying to force other groups to disclose.”

Americans United for Change, which is leading the latest campaign, acknowledges that it receives most of its funding from major labor unions, including the National Education Association, the American Federation of State, County and Municipal Employees (AFSCME) and the Service Employees International Union (SEIU).

But the group is not required to provide a detailed breakdown of its funding to the public because it is a nonprofit group, organized under section 501(c)4 of the tax code, which does not have politics as its “primary purpose.” It reported annual revenue of $4.8 million to the Internal Revenue Service in 2010, which is the most recent filing available.

Adviser Robert Creamer said Americans United “abides by the same standards and rules as all (c)4s” and goes beyond those requirements by identifying the labor groups that support it.

“There are a number of different kinds of organizations that have been involved in campaigns for transparency,” Creamer said. “The point of the current campaign has to do entirely with corporate funds, and our argument that corporations should not be investing shareholder money in trying to influence elections.”

The effort comes amid widespread complaints, particularly among Democrats, about heavy spending in the 2012 contest by super PACs, which reveal their donors, and other outside groups, which do not. A series of legal rulings, including the 2010 Supreme Court decision in Citizens United v. Federal Election Commission, have made it easier for corporations, unions and wealthy individuals to devote unlimited amounts of money to elections.

Groups joining Americans United in the focus on corporate political contributions include Common Cause, Public Citizen, MoveOn.org, Occupy Wall Street, the Campaign for America’s Future, Health Care for America Now, the Public Interest Research Group (PIRG) and the Coalition for Accountability in Political Spending (CAPS).

The allies held a news conference Monday announcing a $25,000 reward to any employee who provides documentation of secret political spending by a corporation. The coalition also said it will use shareholder resolutions, consumer boycotts and other tactics to pressure corporations into either disclosing their political spending or refraining from direct funding of political activities altogether.

The effort “is intended to make CEOs think again if they believe they can keep corporate donations to politics secret,” said Americans United executive director Tom McMahon.

Lisa Gilbert, deputy director of the Congress Watch program at Public Citizen, noted that the nonprofit group lists those who donate $5,000 or more in its annual report. The 2010 version also lists a dozen “trustees” who gave $25,000 or more, including several prominent defense lawyers and one person identified only as “anonymous.”

“We disclose everything we’re required to by law and more,” Gilbert said.

But Collegio said many of the liberal groups involved in the campaign are guilty of “brazen hypocrisy” when it comes to disclosure issues.

“It gets back to the whole reason why private nonprofit corporations aren’t required to disclose their donors to the government,” Collegio said. “It’s a longheld precedent that groups should not be tormented by the state because of the ideology they espouse. But these groups only want that protection when it applies to themselves.”