The Treaties define the scope of the powers of each institution within the EU. The Treaty base is the cause of all EU institutional action. As within all systems of democratic governance, the EU requires its institutions to act within their powers.
The Treaties entrust the CJEU with jurisdiction to review the exercise of powers by EU institutions. It is required to review the choice of Treaty base under which legislation is passed. This requires the Court to consider whether the legislation is adopted under the correct legislative process and whether it is an exercise beyond the powers conferred on the relevant institution.
Note: the procedure under which legislation is passed varies and, depending on which procedure, involves different institutions.