WASHINGTON (AP) — A government watchdog has expanded an ethics probe of the National Labor Relations Board after finding that more inside information was leaked to a former adviser to Republican presidential hopeful Mitt Romney, a Democratic lawmaker said Thursday.

Maryland Rep. Elijah Cummings said the board's inspector general discovered additional and more serious improper disclosures by Republican board member Terence Flynn to former NLRB board member Peter Schaumber, who was a senior labor adviser to Romney's campaign.

Cummings, top Democrat on the House Oversight and Government Reform Committee, said the inspector general referred his findings to the U.S. Office of Special Counsel for potential violations of the Hatch Act, which prohibits federal employees from engaging in partisan political activity.

"If true, the allegations set forth by the inspector general are troubling and raise significant concerns about the extent to which Mr. Schaumber and others may have benefited from these improper, and potentially illegal, activities," Cummings said in a statement.

Romney's campaign disclosed for the first time Thursday that Schaumber stepped down in December from his advisory post, around the time the investigation began. As recently as March, union groups had called on Romney to dismiss Schaumber, and the campaign did not respond when The Associated Press inquired about his status last month.

NLRB spokeswoman Nancy Cleeland said the board's inspector general, Dave Berry, does not comment on pending investigations. Cummings said Berry shared the latest details of his investigation with the committee's Democratic staff.

In March, Berry issued a report finding that Flynn violated ethics rules by revealing confidential details on the status of pending cases, internal analysis of proposed rules and the likely votes of other members before decisions were released. Flynn shared the information with Schaumber and another former board member, Peter Kirsanow, the report said.

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Flynn's personal attorney, Barry Coburn, said he is "unaware of any basis whatsoever for any allegation that Mr. Flynn violated the Hatch Act. His contacts with Mr. Schaumber, his friend and former colleague, were not illegal in any respect."

Flynn was appointed to the board along with two others by President Barack Obama in January. He allegedly committed the violations when he was still a staff lawyer at the agency, before he became one of its five members.

Cummings said Berry plans to issue another report this week detailing the new allegations against Flynn "which he considers even more serious than those outlined in his initial report."

Cummings has called on the oversight committee's GOP chairman, California Rep. Darrell Issa, to conduct interviews with Schaumber and Kirsanow to learn more information. So far, Issa has declined.

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