Environmental Protection Agency Administrator Andrew Wheeler’s chief of staff is leaving the U.S. agency to work for the nation’s top coal mining trade group.

Ryan Jackson is stepping down from his post after three years to become the National Mining Association’s senior vice president of government affairs, the trade group said on Thursday night.

“Mr. Jackson’s in-depth knowledge of the issues and nearly 20 years of working in the U.S. Senate demonstrate a reputation for persistence, integrity, working in a bipartisan fashion,” said Ashley Burke, a spokeswoman for the association, which represents companies such as Peabody Energy Corp. and Alliance Coal LLC.

Because of Jackson’s recent position within the administration, he will be restricted from lobbying the administration for five years and will focus solely on congressional advocacy, Burke added.

Jackson is from Oklahoma and one of several EPA staffers who joined the agency after working for Senator Jim Inhofe, an Oklahoma Republican. His tenure as chief of staff began under former EPA administrator Scott Pruitt.

His departure was reported earlier Thursday by Politico.

Most recently, Jackson has drawn attention because of a dispute with the agency’s inspector general. For months, the office of the inspector general complained that Jackson was not fully cooperating with some of its investigations and openly defying efforts to get more information. The office last year went so far as to issue a rarely used “seven-day letter” formally admonishing Jackson.

Representatives of the EPA did not immediately respond to an emailed request for comment sent after normal business hours.

To contact the reporters on this story: Ari Natter in Washington at anatter5@bloomberg.net;Jennifer A. Dlouhy in Washington at jdlouhy1@bloomberg.net