(CNN) The House Oversight and Government Reform Committee has opened an investigation into Environmental Protection Agency Administrator Andrew Wheeler's compliance with an ethics law that requires officials to disclose all sources of money earned in an amount greater than $5,000 two years prior to holding an appointed position, according to a letter House Oversight chairman Elijah Cummings sent Wheeler.

Wheeler, a former coal lobbyist, did not disclose that he previously lobbied for Darling Ingredients while working at Faegre Baker Daniels Consulting on his financial disclosure forms, according to documents obtained by the committee.

The committee cited the lobbying firm Faegre's quarterly disclosure forms to point out the omission in Wheeler's financial disclosure report. Wheeler "engaged in lobbying activities on behalf of Darling" from April 2015 to May 2016, according to Faegre's forms cited in the House letter to the EPA.

The EPA declined to comment on the committee's request, stating they would respond to the committee through the "proper channels."

The Oversight Committee claims this omission means that Wheeler violated the Ethics in Government Act, which requires federal officials to disclose all money earned in an amount greater than $5,000 in the two years before holding a government position.

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