A flurry of amicus groups on both sides of the class action bar urged the U.S. Court of Appeals for the Ninth Circuit to rehear en banc a decision that they say would effectively nullify nationwide settlements.

Public Justice, the Impact Fund, the American Tort Reform Association and three other groups, plus a law professor and a former federal judge, wrote in briefs filed on Monday that the Ninth Circuit’s Jan. 23 panel decision in In re Hyundai and Kia Fuel Economy Standards would make it next to impossible to certify nationwide settlements. The 2-1 decision de-certified a nationwide class action settlement after concluding that the district judge failed to conduct an analysis over whether consumer laws in several states were so different from one another as to defeat the common claims of class members.