All U.S. employers have the duty to comply with a complex system of immigration laws and related labor laws as they apply to hiring and employing foreign national workers. These range from employment eligibility verification to compliance with nonimmigrant and PERM application programs. U.S. federal agencies may investigate to ensure employer compliance with these rules. Investigations of any employer in the United States, whether or not they employ any non-citizens may be conducted by Immigration and Customs Enforcement (ICE), U.S. Citizenship and Immigration Services (USCIS), U.S. Department of Labor (DOL), and/or the U.S. Department of State (DOS).