Congressional investigators found there was “substantial reason to believe” retiring Rep. Tom Petri (R., Wisc.) may have violated House conflict-of-interest rules for his work on behalf of companies in which he owned stock, according to an Office of Congressional Ethics report released Tuesday.

The report from the ethics watchdog suggested Mr. Petri did not always follow the guidance his office sought from the House Ethics Committee as it related to his advocacy on behalf of defense contractor Oshkosh Corp., a Wisconsin-based firm in which he owned hundreds of thousands of dollars worth of stock. The Office of Congressional Ethics also said his work on behalf of another firm in which he had a financial interest, the Manitowoc Co., may have also violated congressional rules.