Federal Rule of Civil Procedure 24(a)(1) allows “anyone to intervene [in a federal suit] who . . . is given an unconditional right to intervene by a federal statute . . . .” But many of the laws that give a private right to intervene limit that right. The Ninth Circuit recently issued an opinion that shows how the right to intervene plays out in a “host” of federal environmental laws with the same intervention rules.

In 2016, the federal government filed an enforcement action against Volkswagen under the Clean Air Act. The suit was based on Volkswagen’s acknowledgment that some Volkswagen cars had a defeat device that improved emissions test results and violated the Clean Air Act. Like many other federal environmental laws, the Clean Air Act has a three-part citizen-suit provision: Anyone can sue to enforce an emission standard, limitation, or other order under the CAA. But if the federal or a state government is “diligently prosecuting a civil action . . . to require compliance with [that] standard, limitation, or order,” a second, private suit is barred. Anyone who’s private suit is barred then has the right to intervene in the enforcement action under Rule 24(a)(1).

Ronald Fleshman, the owner of a 2012 Jetta, moved to intervene in the government’s enforcement action against Volkswagen. Fleshman claimed that Virginia’s state plan to implement EPA-set standards under the Clean Air Act required Volkswagen to buy back any car with a defeat device. And Fleshman argued that he had the right to intervene under the citizen-suit provision and Rule 24. The district court denied Fleshman’s motion to intervene and he appealed to the Ninth Circuit.

The Ninth Circuit affirmed, holding that Fleshman did not have a right to intervene under Rule 24. As the Ninth Circuit observed, the diligent prosecution bar only applies when the private suit is based on the same “standard, limitation, or order” as an enforcement action. Fleshman’s suit wasn’t barred because his claim was based on Virginia’s implementation plan, which was not part of the federal enforcement action. And under the three-part citizen-suit provision, “a citizen who retains the right to file suit on his own, despite a government enforcement action, has no statutory right to intervene in that action.” Because Fleshman still had a right to file his own suit, he did not have a right to intervene in the enforcement action.

Read the Ninth Circuit’s decision here.