HSI Special Agents have legal authority to enforce the U.S. Immigration and Nationality Act (Title 8), U.S. Customs Laws (Title 19), along with Titles 5, 6, 12, 18 (Federal Criminal Code and Rules), 21 (international drug smuggling), 22, 28, 31 (Money and Finance), 46, 49, and 50 statutes; giving them the broadest federal law enforcement jurisdiction of any agency. HSI has more than 8,500 Special Agents, making it the second largest federal investigative agency within the United States government next to the FBI.
Excerpt from:
http://en.wikipedia.org/wiki/U.S._Immig ... nforcement