Dan Becker, the director of the Safe Climate Campaign at the Center for Auto Safety, a nonprofit Washington research group, said that Volkswagen's new admission was a potential violation of the law. "They put it in their vehicles, and then they signed a certification petition to the regulator saying what they put in their vehicles and didn't mention it," he said. "It's certainly a material omission." Lawmakers did not discuss Volkswagen's admission at length during the hearing. But Representative Fred Upton, Republican of Michigan, openly wondered if Volkswagen was skirting regulations in other ways. "If they were willing to cut corners here, what else have they done?" he asked.