Delegated Regulations, Directives or Decisions, and implementing Regulations, Directives or Decisions are considered as non-legislative acts by the Lisbon Treaty.
Article 290 TFEU on delegated acts allows the European Parliament and the Council of the EU to delegate to the European Commission the power to adopt ‘non-legislative acts of general application to supplement or amend certain non-essential elements of a legislative act’. Non-legislative acts adopted by the European Commission in this way are called ‘delegated acts’. Only ‘non-essential’ parts of a legislative act may be supplemented or amended by the European Commission. The ‘essential’ parts cannot be delegated.
Article 291 TFEU introduced the concept of implementing acts which is related to delegated acts. The ‘delegated act’ is defined, in terms of its scope and consequences, as a general measure that supplements or amends non-essential elements; whereas the ‘implementing act’ is determined by its rationale, the need for uniform conditions for implementation. In the system introduced by Article 291 TFEU (implementing acts), the European Commission does not exercise any ‘quasi-legislative’ power; its power is purely executive. Primary responsibility in implementing EU laws lies with the Member States, but because it is necessary to have uniform implementing conditions, the European Commission must exercise its executive power.