The Office of Congressional Ethics is examining New York Rep. Chris Collins’ role in attracting U.S. investors to an Australian biotech company in which he is the largest shareholder, The Buffalo News reported Tuesday.

The story cited unnamed sources who told the newspaper that the office began sending letters to investors seeking information about a month ago. Legally, they are not required to provide it or submit to interviews.

The ethics office investigators interviewed several investors from the Buffalo, N.Y., area on Monday and Tuesday, according to the story. Collins, a Republican who is a prominent ally of President Donald Trump’s, represents a district in the Buffalo area.

The newspaper said the probe focuses on investments in Innate Immunotherapeutics, a company whose stock Collins first bought in 2005. Others with ties to Collins — some of them campaign donors — later became investors, too. They included executives at Buffalo-area companies and institutions, such as a physician at Roswell Park Cancer Institute in Buffalo.

Collins’ spokesman said in a statement that his boss had done nothing wrong.

“Despite the continued partisan attacks insinuating otherwise, Congressman Collins has followed all ethical guidelines related to his personal finances during his time in the House and will continue to do so,” Collins aide Michael Kracker said.

The company fell into a political controversy late last year when former congressman Tom Price — now the secretary of Health and Human Services — was identified as an investor. News reports about Collins’ and Price’s holdings in Innate raised questions about whether they benefited from legislation that could help Innate.

Price said at his confirmation hearing this year that he bought Innate stock after Collins told him about the company. He later sold the stock as he had promised, Price disclosed recently, and reportedly tripled his investment.

Public Citizen, a government watchdog group, asked the ethics office to open an investigation into Collins’ activities in February, citing a Kaiser Health News story about the congressman. The office has received at least four complaints about Collins’ involvement with Innate, The Buffalo News reported.

Sources told the newspaper that they were unsure whether the ethics probe would lead to further action. Most investigations do not, the Office of Congressional Ethics has said.

If it finds wrongdoing, the office can refer allegations to the House Committee on Ethics for potential disciplinary action.