Normally, states aren't allowed to set their own emissions rules for cars and trucks—federal law reserves that to the EPA (the agency that regulates air pollution and vehicle standards nationwide). But California has long had special permission, called a waiver, to write stricter rules than the federal government, covering things like how long truck engines must be warrantied for emissions parts and requirements pushing manufacturers toward zero-emission delivery trucks, shuttle buses, and similar vehicles. This resolution would cancel that permission, meaning California could no longer enforce these specific stricter truck and engine emissions rules it had been granted the right to apply. This mainly affects truck and engine manufacturers, fleet operators, and anyone in California (or other states that often follow California's rules) who would otherwise have been subject to these tougher standards.