Ok. This is like a batsignal to me.
I suspect that the agencies you are thinking of were born post-New Deal.
The problem there is (and I forget the case/cases), that SCOTUS basically decided that if Congress and POTUS want to pass legislation that abdicates responsibility for "rule-making" and enforcement from both of them to an agency, and the agency passes rules that would otherwise be constitutional, and enforces them in ways that are constitutional, then the separation of powers/checks and balances provisions of the constitution allow it.
It is not what the constitution intended. But is constitutional.
