I am not a lawyer, but in US the federal law consists of 2 parts: US Code (USC), and Code of Federal Regulation (CFR).

The USC is created and maintained by the Congress. USC delegates to federal agencies implementation of USC through CFR, i.e. by writing it. Any changes to CFR, should be published and given a comment period, my understanding that it's 6 months. During this time, the Congress has option to review, and disapprove changes to CFR if they see that it makes sense. (Others could also write comments and send them to the federal agency).

My non-lawyerish understanding is that this describes proposed changes to CFR within the authority delegated by the congress.