Authorized officials have extensive powers of investigation. For example, they are empowered by Article 20(2) of Regulation No 1/2003 to enter all premises, land and means of transport of undertakings and associations of undertakings for the purpose of the inspection. Offices located in a place other than the head office are considered as premises of the undertaking, to which the officials have access, provided that the undertaking carries out its business there. Similarly, the Commission may gather evidence by conducting an inspection at premises belonging to a different undertaking than the one to which the inspection decision is addressed, when the premises of the inspected undertaking have been used by the addressee undertaking to develop its business activities and the two undertakings form one and the same economic unit.

Article 21 of the Regulation also authorizes the search for evidence at any premises where the Commission suspects the possession of books or other business records relevant to the subject matter of the inspection, which may be relevant to prove a serious infringement. In this case, the inspection may take place at any premises, land and means of transport, where such documents are held, including the homes of directors, managers and other members of staff of the undertakings and associations of undertakings concerned. The inspection must be by way of formal decision, which must state the reasons for it. It must specify the subject-matter and purpose of the inspection, in particular by stating the reasons that have led the Commission to suspect that a serious infringement exists. The decision must also set out the start date of inspections and mention the right for undertakings to have the decision reviewed by the General Court. The Commission must first consult the competition authority of the Member State in whose territory the inspection is to be conducted. Furthermore, the decision cannot be enforced without prior authorization from the national judicial authority according to the same terms and conditions as the inspection ordered by decision.