EPA has never banned small trucks. This is from consistent misinformation that shifts blame from car manufacturers to the government.

EPA made a scaled plan that required improvements to emissions from smaller trucks first, then larger trucks over the years.

Car manufacturers chose to abuse that flexibility by simply not making smaller trucks, instead of making ones that meet the standards, which is why trucks have steadily inflated in size in the US as they make whatever the next unregulated size class is that year.

You can of course partially blame EPA for not having the foresight to predict that would happen - but they also make regulations under pressure from politicians and lobbyists who are themselves influenced by car manufacturers.

The emissions laws they have in place isn't really a ban but instead just less encouraging of smaller trucks. The bigger the truck the emissions get easier to pass.

https://newrepublic.com/article/180263/epa-tailpipe-emissions-loophole

I believe that the OP means the Imported Vehicle Safety Compliance Act of 1988, which effectively bans kei trucks from import into the U.S. because they're not manufactured to the Act's standards.

Or, perhaps the Chicken Tax, a 25% tariff imposed on the import of light trucks in 1964 as part of trade dispute with Europe. It's still in effect, shielding American manufacturers from competition from smaller, lighter trucks.