Excerpt from the U.S. table of spectrum allocations GPS Spectrum and Interference Issues

The Global Positioning System uses radio signals in frequencies (spectrum) reserved for radio navigation services. Ensuring the continuity of the GPS service requires protection of this spectrum from interference. GPS interference can come from a variety of sources, including radio emissions in nearby bands, intentional or unintentional jamming, and naturally occurring space weather.

The U.S. government works to minimize human sources of GPS interference through spectrum regulations (domestic and international), interference detection and mitigation efforts, and law enforcement.