Federal prosecutors have charged a lobbyist and his Alexandria firm with violating federal lobbying law by failing to submit dozens of disclosure reports, a rare legal move that could carry a fine of as much as $5.2 million.

The civil complaint, filed by the U.S. Attorney’s Office for the District of Columbia, alleges that Alan Mauk and his firm, Alan Mauk Associates, did not file required quarterly lobbying reports at least 13 times between 2009 and 2013. They are also charged with failing to file semi-annual reports on political contributions on at least 13 occasions, also in violation of the Lobbying Disclosure Act. The law carries a fine of up to $200,000 for each violation.

Mauk, the only registered lobbyist in his firm, responded to the charges in an e-mail sent Tuesday. “My lawyer and I will address the charges but I will do everything I possibly can to correct any errors that I may have made in filling my reports,” he wrote.

According to records Mauk filed, the firm represented just a handful of clients during the period under review. Mauk reported just $10,000 in income and three clients in 2013, including the Chickasaw Nation and the Oklahoma Department of Transportation. House and Senate officials notified him at least 22 times about the missing reports, according to the civil complaint, which was filed Friday and first reported by Legal Times.

Such legal action against lobbyists is rare, but it has been increasing.

Last June, the U.S. Attorney’s Office for the District of Columbia filed a civil suit against Biassi Business Services, a New York consulting firm, charging it with 124 disclosure violations. In 2012, prosecutors reached settlements with two lobbying firms for repeated violations of the disclosure law. Lussier, Gregor, Vienna & Associates agreed to pay a civil penalty of $50,000, and the Da Vinci Group agreed to pay a civil penalty of $30,000.

“The American people deserve to know who is spending money to lobby our Congress,” U.S. Attorney Ronald C. Machen said when the 2012 settlements were announced. “When lobbyists fail to report their activities, they deprive the public of crucial information and undermine confidence in the legislative process.”

Fred Dombo, a lobbyist at Nossaman LLP who also advises clients on lobbying laws, said the recent cases “show that the Justice Department is getting serious about enforcement of federal lobbying requirements.”

Lee Drutman, a lobbying expert at the Sunlight Foundation, a nonprofit that advocates for greater government transparency, said the cases will “hopefully send a signal to any other lobbying firm that is not being forthright in disclosing its activities.”