Despite criticism of Fannie Mae by Republican presidential candidate Mitt Romney, his campaign accepted nearly $280,000 in donations raised by a registered lobbyist who once represented the government mortgage giant and whose clients now include a private equity firm and the drug company Pfizer.

Yet Romney has not identified all of his so-called fundraising “bundlers” who have raised hundreds of thousands of dollars, even after President Barack Obama’s re-election campaign released the names of his top fundraisers. Rick Santorum and Newt Gingrich also haven’t disclosed their bundlers. Ron Paul’s campaign has said it doesn’t use them. For more than a decade, since the election of George W. Bush in 2000, presidential campaigns have identified their bundlers.

In an age of “super” political action committees, which can pull in millions of dollars from anonymous donors, bundlers still matter to modern presidential campaigns. Like Wayne Berman, the chairman of Ogilvy Government Relations and former Fannie Mae lobbyist who gathered $279,075 for Romney in 2011, these are well-connected executives who collect or direct multiple individual contributions of up to $2,500 to a campaign in amounts that can range from $50,000 to more than $500,000.

The lack of disclosure prevents voters from knowing who wields influence within a presidential campaign. Keeping their identities secret could end up stinging Romney — like the mishandled release of his income tax returns — if voters conclude he is withholding politically damaging information.

Federal law requires only that candidates disclose the identities of bundlers who also are registered lobbyists, which the Romney campaign has done. Berman and 15 other lobbyists representing a wide range of interests raised nearly $2.2 million for Romney in last year, according to Federal Election Commission records. Their clients included investment firms and a mortgage processing company accused of “robo-signing” foreclosure documents.

But just as disclosing income tax statements is commonplace for leading presidential candidates, voluntarily identifying bundlers has also become standard practice.

A corporate executive or a Wall Street broker who acts as a bundler can wield just as much influence as a lobbyist.

Paul Ryan, associate legal counsel at the nonprofit Campaign Legal Center, said the rise of super PACs, which can’t lawfully coordinate their spending with a candidate’s campaign, haven’t diluted the importance of bundlers. “At the end of the day, candidates want money in their own campaign accounts because they have full control over how it is spent,” he said.