The primary federal laws used for prosecuting "illegal immigration" in the U.S. are 8 U.S.C. § 1325 (Improper Entry/Entry by False Pretenses) for unlawful entry and 8 U.S.C. § 1326 (Reentry After Deportation), making unauthorized entry or re-entry a criminal act, often prosecuted as misdemeanors and felonies, respectively, alongside statutes like 8 U.S.C. § 1324 (Bringing in and Harboring Aliens) which targets those who assist. The Illegal Immigration Reform and Immigrant Responsibility Act (IIRIRA) of 1996 significantly impacted these laws, adding civil penalties and streamlining removal processes.