AnalogDiehard writes: The recent — and questionable — practice of technological and pharmaceutical companies selling their patents to US native indian tribes (where they enjoy "sovereign immunity" from the inter partes review (IPR) process of the PTO) then the tribes licensing them back to the companies is drawing scrutiny from a federal court and has inspired a new US bill outlawing the practice. The IPR process is a "fast track" (read: much less expensive) process through the PTO to review the validity of challenged patents — it is loved by defendants and hated by patent holders. Not only has US Circuit Judge William Bryson invalidated Allergan's pharmaceutical patents due to "obviousness", he is questioning the legitimacy of the sovereign immunity tactic. The judge was well aware that the tactic could endanger the IPR process which was a central component of the America Invents Act of 2011 and writes that sovereign immunity "should not be treated as a monetizable commodity that can be purchased by private entities as part of a scheme to evade their legal responsibility." US Senator Claire McCaskill (D-Mo.) — no stranger to abuses of the patent system — has introduced a bill that would outlaw the practice she describes as "one of the most brazen and absurd loopholes I've ever seen and it should be illegal." Sovereign immunity is not absolute and has been limited by Congress and the courts in the past. The bill would apply only to the IPR proceedings and not to patent disputes in federal courts.