Petri said he was simply representing his constituents.
"Articles (enclosed) recently questioned my ownership of stock in companies and my actions on their behalf," he said in the letter. "It is my honor and duty to advocate on behalf of those who live and work in my area; I am distressed by the innuendo in these articles."
The value of Petri's Oshkosh stock increased by 30 percent while he was advocating for the company to secure a Defense Department contract and pushed Congress to reject cuts to the Pentagon's budget, according to Gannett.
In his letter, Petri said that he disclosed information on his personal finances and consulted the Ethics Committee about advocating for Oshkosh.
Ethics rules prohibit representatives from using their public office for personal gains, but the committee decides the maters mostly on a case-by-case basis, according to USA Today.