WASHINGTON—An investigation targeting President Trump’s top emergency-management official has been referred to federal prosecutors to determine whether criminal charges should be pursued, according to people familiar with the probe.

Brock Long, the administrator of the Federal Emergency Management Agency, and two other federal employees may have broken as many as six laws as they commuted frequently between Washington and Mr. Long’s home in Hickory, N.C., at taxpayers’ expense, said one of the people briefed on the investigation.

Mr. Long has said he is cooperating with the investigation, which has been led by the Department of Homeland Security’s inspector general. Mr. Long declined to comment through a FEMA spokesman.

The inspector general’s office and U.S. attorney’s office in Washington also declined to comment. A White House spokesman didn’t return a request for comment.

On Monday, House Oversight Committee Chairman Trey Gowdy (R., S.C.) asked Mr. Long for documents related to each of his trips home and any communications with FEMA employees who traveled with him.