A bureaucrat's opinion of a law is completely irrelevant. If the intent is unclear they can ask the legislators what they intended. If those lawmakers are dead, well that is why we need a sunset provision, but they can ask current lawmakers, or a court. The agency's this informed interpretation should never hold any weight in court. It's precisely this kind of centralized power that has allowed the FCC to impose taxes without any vote and the EPA and DoE to start carrying guns without any legal justification.