California has an air pollution agency, the California Air Resources Board, which writes rules for the state, and it had asked the federal Environmental Protection Agency (the national agency that enforces pollution laws) for permission to expand a rule about ships parked at its ports. That rule limits the emissions from the auxiliary engines that ships keep running for power while docked, and the expansion would have applied it to more types of ocean-going vessels. The EPA granted that permission, and this resolution would use Congress's power to cancel a federal agency's decision, wiping out the approval so California could not enforce the expanded version of the rule. The summary does not say what would happen beyond that, such as how ports or shipping companies would respond, so those effects are left unstated.