It's called nondelegation doctrine. The rulings pertaining to it have not been consistent but it generally holds true.

https://www.law.cornell.edu/wex/nondelegation_doctrine

I’ve seen some discussion about that topic but I’ve found it hard to parse what people think of as far as how explicit they expect congress to be. At some point it seems unworkable/ a recipe for very inflexible government policy.

Yes, they are an unelected executive branch bureaucracy. They don't have the authority to invalidate long-standing labor laws arbitrarily.