On February 15, 2019, Leon dismissed a lawsuit brought by the North American Butterfly Association against the Department of Homeland Security (DHS) seeking to prevent the building of a border wall through its National Butterfly Center, a 100-acre wildlife preserve in the Rio Grande Valley in Texas. He said the Fourth Amendment against unreasonable searches and seizures "offers little refuge for unenclosed land near one of the country’s external borders" and that environmental review had been properly waived by the DHS.