From SCOTUSBlog here.
On Tuesday in United States v. Cooley, the Supreme Court upheld a power that tribal governments have long assumed they possessed as a basic necessity of ensuring public safety. The court held that tribal governments — and thus their police officers — retain the power to temporarily stop, and if necessary, search non-Indians traveling on public rights-of-way (highways) through reservations for suspected violations of federal or state laws. The unanimous opinion was authored by Justice Stephen Breyer. The decision represents an important affirmation of tribal inherent sovereign power by the new court and the first time the court has ever found that a tribe’s interest in addressing a threat to its political integrity, economic security, health or welfare was strong enough for the tribe to exert government authority of any kind over a non-Indian.