I cant vouch for the accuracy of the site. You might want to investigate for yourself.I believe that the law has been in place since 1979 but enforcement has been lax.
Alta Mini Performance - Replacement Catalyst w/ Header
What should customers know about buying converters for their cars?
First and most importantly, the original converter on a car or truck was designed to last the life of the vehicle if it is properly used and maintained, and is fully warranted by the vehicle manufacturer to last for at least 5 years or 50,000 miles (8 years or 80,000 miles on 1995 and newer cars and trucks ), whichever comes first. See the vehicle warranty booklet for more information.
It is illegal to remove a functional catalytic converter even to replace it with a new one.
It is illegal to tamper with emission control devices. The Anti-tampering Law applies to individuals as well as to businesses. Individuals may be fined as much as $2,500 for each vehicle tampered with, and businesses are subject to fines of up to $25,000.