I think you meant legislative process. Departments and government agencies like DOJ write regulations. Some regulations exceed legislative authority and are often challenged. West Virginia won a case against the EPA for clean water regulations that exceeded legislative intent under the clean water act.
What I meant was that an agency cannot give itself powers through a regulatory action that were not granted to it by Congress. Even then there is a constitutional limit that Congress imposes, whether it poses a major questions doctrine - some powers Congress cannot give away.