Fight for $15 workers protest the nomination of Andy Puzder for labor secretary on January 26, 2017 in Chicago, Illinois.

Andy Puzder, the fast-food restaurant chief executive nominated to be labor secretary, hired an undocumented household employee, further challenging his nomination to run the Labor Department, NBC News confirmed Monday night.

His use of undocumented household help could be another strike against Puzder, who has been fiercely opposed by Democrats because of his role leading a fast food chain, CKE restaurants, which runs Hardees, Carl's Jr. and other chains.

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Puzder notified the Trump administration of his employee, and the White House official passed on a statement from Puzder.

"My wife and I employed a housekeeper for a few years, during which I was unaware that she was not legally permitted to work in the U.S. When I learned of her status, we immediately ended her employment and offered her assistance in getting legal status. We have fully paid back taxes to the IRS and the State of California and submitted all required paperwork regarding her employment," Puzder said in the statement.