6 U.S.C. § 202: Border, maritime, and transportation responsibilities

Preventing the entry of terrorists and the instruments of terrorism into the United States. Securing the borders, territorial waters, ports, terminals, waterways, and air, land, and sea transportation systems of the United States, including managing and coordinating those functions transferred to the Department at ports of entry. Carrying out the immigration enforcement functions vested by statute in, or performed by, the Commissioner of Immigration and Naturalization (or any officer, employee, or component of the Immigration and Naturalization Service) immediately before the date on which the transfer of functions specified under section 251 of this title takes effect. Establishing and administering rules, in accordance with section 236 of this title , governing the granting of visas or other forms of permission, including parole, to enter the United States to individuals who are not a citizen or an alien lawfully admitted for permanent residence in the United States. Establishing national immigration enforcement policies and priorities. Except as provided in part C of this subchapter, administering the customs laws of the United States. Conducting the inspection and related administrative functions of the Department of Agriculture transferred to the Secretary of Homeland Security under section 231 of this title . In carrying out the foregoing responsibilities, ensuring the speedy, orderly, and efficient flow of lawful traffic and commerce.