Of all the new ethics and lobbying restrictions enacted on Capitol Hill in the wake of the Jack Abramoff scandal, lobbyists have always been particularly worried about the so-called bundling disclosure rules.

Until now, lobbyists have had the luxury of ignoring those requirements, which were a centerpiece of the Honest Leadership and Open Government Act of 2007. That's because the Federal Election Commission took more than two years to issue regulations implementing them, a delay due in part to a prolonged commission shutdown following a Senate dispute over appointments.

But last month the FEC finally approved guidelines explaining exactly how the bundling disclosure requirements will work. The rules require lawmakers, political party committees and leadership PACs to report any political contributions that lobbyists bundle, or round up, on their behalf. The first reporting deadline kicks in on May 20. That means any donations that lobbyists bundle for lawmakers in April will be included in those reports.

A little-noticed side effect of the new bundling regulations may be to shed fresh light on so-called leadership PACs.

Lobbyists fret that the resulting disclosures will provide fresh fodder to journalists, watchdogs and investigators looking to connect the dots between political donations and legislative action -- even when no connection exists.

"When you take all these new disclosure schemes -- which are all online, which are all downloadable, which are all sortable -- the lobbyist community and their clients face a heightened risk," Stefan C. Passantino, head of the political law team at McKenna Long & Aldridge, told National Journal earlier this year.

Good-government advocates retort that lobbyists should have no trouble getting around the rules. They maintain that the FEC's bundling regulations actually provide lawmakers and lobbyists a road map for evasion. Reform advocates were outraged that the FEC did not require disclosure of all lobbyist-bundled donations made with the lawmaker's knowledge, as the original 2007 law required.

Instead, the commission requires disclosure only when the lawmaker (or committee) acknowledges the bundled donations through a formal tracking system, or through tokens of appreciation such as a signed photograph.

Lawmakers can also get around the disclosure rules by raising bundled money from multiple lobbyists at the same event, critics say. Lawmakers must report only donations that reach a threshold of $16,000 in either the first half or the second half of the year. If several lobbyists got together to bundle $16,000, for example, the FEC regulations say the candidate would not have to report that.

"Each lobbyist co-host at a fundraising event should be attributed with having jointly raised the total amount," said Paul S. Ryan, FEC program director at the Campaign Legal Center. The law's authors, including Sen. Russell Feingold, D-Wis., and then-Sen. Barack Obama, explicitly spelled out a more stringent interpretation than the FEC's when they enacted the law, Ryan noted.

Still, both lobbyists and lawmakers have a right to be nervous about the FEC's new bundling regulations. That's because the rules are unusually vague about certain definitions, say election lawyers. For example, the rules apply not just to lobbyists, but to lobbyist-controlled PACs that engage in bundling. But it's not always clear just what constitutes a lobbyist-controlled PAC.

According to the FEC regulations, a PAC is controlled by a lobbyist if the lobbyist has a "primary role" in setting up the PAC, or directs its "governance or operations," noted Lawrence H. Norton, of counsel to Womble Carlyle Sandridge & Rice. The FEC instructs those with questions to consult the secretary of the Senate and the clerk of the House, which have signaled that a PAC is lobbyist-controlled if a PAC board member or treasurer is a lobbyist.

"That leaves an awful lot of gray area," said Norton, who was previously general counsel to the FEC. "What if there's not a formal board? What if you actively participate in decisions, but you're not formally a member of the board? And what does 'establish' mean?" He added: "The rules are convoluted and difficult to enforce."

A little-noticed side effect of the new bundling regulations may be to shed fresh light on so-called leadership PACs, which have exploded despite controversy in recent years. Lawmakers often register their personal PACs under generic-sounding names that give no clue who controls them. But the new bundling rules for the first time require leadership PACs to file amended forms identifying themselves as such. Already, more than half a dozen new leadership PACs have come to light, including the House Conservatives Fund, sponsored by Rep. Patrick McHenry, R-N.C., which collected more than $1 million in the 2008 cycle.

Norton acknowledged that some politicians will simply acknowledge bundling with a wink and a nod, and that some lobbyists will skate under the reporting threshold by rounding up no more than $16,000 in any six-month period. "I think that you're going to see a proliferation of micro-bundlers," he predicted.

Still, the new bundling rules represent just one more danger zone for lobbyists at a time of heightened ethics sensitivity in Washington. First, they'll have to figure out just what the new regulations mean. Then they'll have to figure out just how badly they want credit for their bundled contributions. Noted Norton: "At the very least, there will be information in the public domain that wasn't previously there."

Want to stay ahead of the curve? Sign up for National Journal’s AM & PM Must Reads. News and analysis to ensure you don’t miss a thing.