A little-noticed provision in the lobbying reform overhaul passed last month by the House could have serious unintended consequences: roiling K Street by knocking some of its biggest players out of the game.

Firms — no less than reigning downtown king Patton Boggs — could see their lucrative lobbying practices sidelined if the measure survives House and Senate conference negotiations in its current form.

The provision, authored by Rep. Chris Cannon (R-Utah), was meant to target firms whose lawyers collect taxpayer dollars working for Congressional panels.

But it was drafted too broadly — a fact even Cannon has acknowledged.

Beyond impacting hired guns freelancing for committees — a relatively rare phenomenon — the provision also appears to capture lawyers doing any kind of legal work for Members of Congress or Capitol Hill staffers, even personal matters that officials pay for out of their own pockets.

Under the bill, a law firm engaging in legal work for a Member of Congress or staffer would be banned completely from all Congressional lobbying for the duration of the contract, plus a year after it ends. And the prohibition applies retroactively, meaning that a lobbying firm that has provided recent legal advice to Capitol Hill would have to terminate all its lobbying contracts by the time the reform bill becomes law, or face possible criminal prosecution.

Besides Patton Boggs, firms that could have to clear their rosters of lobbying clients include downtown heavyweights Akin Gump Strauss Hauer & Feld; McKenna Long & Aldridge; and Wiley Rein, all of which have been paid for doing legal work for Members this year.

Under the House bill, as currently drafted, a firm would have to choose between offering legal work and continuing its lobbying practice. “Under this provision, if we represented a staffer in a divorce proceeding, we couldn’t lobby for years,” said Frank Donatelli, a partner with the law and lobbying firm McGuireWoods.

Since firms with even limited lobbying practices reap relatively large payouts from the work, several lawyers said most law firms would unlikely opt for continuing to offer legal and investigative help to those on Capitol Hill. Practically, then, the measure would make it very difficult for lawmakers and staff to find legal representation at the city’s most prominent law firms, almost all of which have lobby practices, forcing them to choose smaller firms which do not lobby, but which also might not have the legal specialities they need.

Hubbub over the change started percolating downtown last week, as K Streeters scanned the House bill and began realizing its potential reach.

Brian Pallasch, president of the American League of Lobbyists, said it came up at a Thursday briefing on the lobbying reform bill and ranks near the top of his group’s concerns.

It may be much ado about nothing. Cannon spokesman Fred Piccolo said the Utah Republican wants House and Senate negotiators to narrow the focus of the provision to outside lawyers receiving federal money to assist Congressional panels in their work.

Indeed, Cannon’s measure apparently was prompted by one lawyer, Irvin Nathan, a partner at Arnold & Porter, who is collecting as much as $25,000 a month helping Democrats on the House Judiciary Committee with their investigation of the scandal surrounding the firings of U.S. attorneys — while his firm lobbies on behalf of other clients before the same panel.

Cannon is the ranking member of the Judiciary panel’s subcommittee on commercial and administrative law, the lead subcommittee on the U.S. attorneys investigation.

“If federal funds are used to pay a lawyer or law firm, they have to pick whether they want to do that work or lobby. They can’t do both,” Piccolo said. The aim, he said, is to prevent Congress from “shelling out money for high-priced lawyers, when that’s what they pay staff to do.”

Meanwhile, Piccolo said, Cannon recognizes that his provision, which Judiciary panel members adopted on a voice vote with little debate, is open to a much broader interpretation than the one he intended. “If clarification language needs to be added, Rep. Cannon would not be opposed to that at all.”

He said Cannon is likely to raise the issue of clarifying language himself with conferees. A simple fix could involve inserting language specifying that the provision only addresses contracts paid with federal money, and not funds from a staffer or lawmaker’s personal or campaign accounts.

Spokesmen for Speaker Nancy Pelosi (D-Calif.) and House Judiciary Chairman John Conyers (D-Mich.) did not return calls for comment.

Senators did not include a similar provision in a lobbying reform bill they approved earlier this year, and several lawyers and lobbyists predicted the measure could get struck entirely during negotiations with the Senate.

But major lobbying firms in the cross hairs aren’t taking that for granted. James Christian, a partner at Patton Boggs, said his firm already has raised the issue with Cannon’s office. “At the moment, I’m not terribly concerned, because the author of the amendment has indicated he wants to clarify the language to better reflect his intent,” Christian said. If a fix doesn’t come together, he said, firm officials would take it up with other lawmakers.

Christian’s firm pulled in more than $35 million in lobbying fees in 2006, according to CQ PoliticalMoneyLine, making it far and away the biggest lobby shop in town. The firm has collected much smaller amounts providing legal counsel to lawmakers.

During the first three months of this year, it earned $26,000 from Rep. Tom Reynolds (R-N.Y.) for work related to the former Rep. Mark Foley (R-Fla.) investigation. Rep. Tom Feeney (R-Fla.) paid Patton Boggs $23,000 for legal help over a jaunt he took to Scotland in 2003 with now-incarcerated ex-lobbyist Jack Abramoff. And Rep. Rick Renzi (R-Ariz.), under investigation for a land deal, reported more than $103,000 in debt to the firm.

Christian said even in a worst-case scenario — in which the measure remains intact and unchanged through conference negotiations — his shop likely would not dump its lobbying clients to comply with the provision’s backward-reaching terms. Instead, he said, if challenged, the firm would answer by pointing to the more limited intended scope of the measure.

Legal experts agreed that beyond any other problems the provision might spawn, its retroactive terms would be unlikely to survive a legal challenge.

“The Constitution clearly prohibits retroactive application of criminal laws,” said Brett Kappel, an election law specialist with Vorys, Sater, Seymour and Pease.

If nothing else, the flap over the Cannon measure points up the difficulty of drafting lobbying and ethics reforms with nobody to vet or interpret the legislation, said Ken Gross, a lawyer with Skadden, Arps, Slate, Meagher & Flom, referring to the frantic few days leading up to the bill’s 396-22 passage by the House on May 24.

“We were fortunate enough to have this issue raised prior to the conference,” Gross said. “But you know, sure as shootin’, there are going to be other ones discovered after the president signs the bill.”

Other issues loom for conference negotiators as well. Most importantly, they will need to reconcile the two chambers’ very different approaches to the issue of the revolving door.

The Senate bill doubles the current one-year cooling-off period for lawmakers and staff who take lobbying jobs. And it expands the scope of prohibited activities during that time off from direct contact with former colleagues to include backroom strategizing. House leaders originally proposed simply doubling the cooling-off period but were forced to dump the provision in the face of stiff resistance from rank-and-file Members, who complained the measure would make it much tougher for them to find jobs on K Street after serving in Congress.