Petri, a Republican from Fond du Lac, asked for the probe after Gannett reports in February drew a link between companies that have business before Congress and the amount of stock he owns in those companies.
In his latest campaign finance report, Petri listed three payments to the Washington, D.C., law firm Covington & Burling LLP, which is representing him in the ethics probe. The payments, totaling $137,321, came from campaign funds.
House rules say it's generally permissible for members to use campaign funds to defend themselves in cases that involve campaigning, electioneering or the performance of official duties. And the House Ethics Committee approved his use of campaign funds for his legal defense, Petri's office said in a statement.
In February, Petri, 74, wrote a letter to the U.S. House ethics committee in February asking it to review the matter while defending his actions, saying he has always been transparent.
Two months later, he announced he was retiring in January after a 35-year career, even though his staff had said he'd been planning to run for one more term. He'd generally won elections with ease in his Republican-leaning district and had faced only two GOP primaries, but he would have had a primary challenge this year from more conservative candidates.
Petri's request for the ethics investigation referenced a number of articles from Gannett Wisconsin Media's Washington bureau.
One article reported that Petri bought hundreds of thousands of dollars' worth of stock in Oshkosh Corp. and then pressed colleagues to help the company retain a $3 billion military contract and avoid Pentagon cuts.
A second said Petri and his wife owned shares worth between $65,000 and $100,000 in a timber company that was pushing for a bill before Petri's transportation subcommittee. The bill would have increased weight limits for trucks on federal highways, a move that would allow the company to load more timber on each truck.
If the ethics investigation is still going on when he retires, the probe will immediately cease because the House Ethics Committee would no longer have jurisdiction.
That's similar to what happened earlier this year with former U.S. Rep. Trey Radel. An investigative subcommittee began a probe after the Florida Republican pleaded guilty to a misdemeanor charge of possessing cocaine, but the investigation ended when he resigned.