The Environmental Protection Agency has accused four muffler-repair shops and a taxicab firm of violating the Clean Air Act by removing catalytic converters from cars. The agency has proposed levying fines, ranging from $12,500 to $120,000, against shops in Covington, Ky., Memphis, Tampa and Sarasota, Fla., and the Sun Lines Cab Co. in Fort Myers, Fla. The companies are accused of removing a total of 131 converters.

The Clean Air Act prohibits commercial repair facilities and fleet operators from removing any air pollution devices, said Kathleen M. Bennett, assistant EPA administrator for air, noise and radiation. If the companies contest the fines, the EPA will refer the charges to the Justice Department for prosecution. Bennett said 40 states prohibit the removal of pollution devices, but few enforce the law.

According to the EPA, it has hired a private firm and state and local agencies to perform up to 17,000 inspections per year. It also frequently calls upon 22 EPA investigators to check for tampering. The agents are described as making unannounced visits to shops that are reportedly willing to remove pollution control devices. Recent EPA surveys found that 20 percent of all cars have had emission controls removed or altered.

Motorists who remove catalytic converters because they believe it will make their cars run better are "deceiving themselves," Bennett said. "New cars are designed with the catalyst as an integral part of the system," she said. "Removing the catalyst upsets that balance."