The "Stop Illegal Fishing Act" seeks to combat illegal, unreported, and unregulated (IUU) fishing by requiring the President to impose sanctions on foreign persons and vessels involved in these activities. Specifically, sanctions would target individuals who own, captain, or serve as senior crew on vessels engaged in IUU fishing, as well as entities primarily involved in such practices and their officers or senior managers. The bill emphasizes that IUU fishing is a significant driver of overfishing, damages marine ecosystems, undermines economic security, and is often associated with forced labor and inhumane treatment of crew. The mandated sanctions include the blocking of assets within U.S. jurisdiction and the denial or revocation of visas for foreign persons identified as engaging in IUU fishing. The President is also required to establish an IUU fishing sanctions program and submit annual reports for five years detailing implementation efforts and listing sanctioned entities. Exceptions to these sanctions are provided for humanitarian assistance, international obligations, intelligence activities, and actions necessary for the safety of vessels and crew.