The Office of Congressional Ethics, which serves as a grand jury of sorts conducting preliminary investigations, said that Mr. Petri’s office had in fact sought permission in 2009 to write a letter to the Defense Department related to the contract dispute, but that Mr. Petri had agreed not to mention Oshkosh by name. But in the letter he signed, Oshkosh was named.

Mr. Petri also contacted the Environmental Protection Agency in August 2013 on behalf of Manitowoc, another Wisconsin company, asking the agency to grant it a “hardship exemption” that would allow it to continue to use diesel-engine cranes it manufactures, based on a concern that switching to more environmentally friendly engines would cost the company jobs.

Mr. Petri’s staff acknowledged that he did not notify the E.P.A. of his shares in Manitowoc or seek Ethics Committee advice on his intervention before it took place, the report says. Mr. Petri, as of December 2013, owned $250,000 to $500,000 in stock in the company, meaning his action in this case may have been an ethics violation as well.

House rules do not prohibit lawmakers from voting on an issue that might have an effect on a company they own stock in, such a prohibition being seen as impractical. But lawmakers are supposed to take extra caution when intervening with a federal agency or introducing legislation that has a direct effect on a company they are heavily invested in, particularly if they could profit as a result.

A similar question came up in the 2012 case involving former Representative Shelley Berkley, Democrat of Nevada. The Ethics Committee concluded then, when it admonished her, that “it is improper to provide official assistance to entities in which the member has a significant financial interest.” That case involved her intervening with the federal authorities related to a medical practice her husband co-owned.