[dragonwriter]

> and then the law would get struck down because, as said, washington state isn't allowed to regulate interstate commerce.

It isn't allowed to discriminate against or unduly burden interstate commerce; it can generally regulate the behavior of Washington persons (including corporations) in interstate commerce where such regulation does not discriminate against such commerce (which is clearly the case where the rule is identical to that for in-state commerce of the same type.)

The exception would be if the federal government preempted the kind of regulation Washington sought to make by exercise of federal commerce powers.