The principle of proportionality, guaranteed by Articles 49 and 52 of the Charter of Fundamental Rights of the European Union, requires that the means used to attain a given end should be no more than what is appropriate and necessary to attain that end. A measure is considered compatible with the principle of proportionality if it pursues a legitimate aim and if the means employed are both necessary and the least burdensome  in other words, the minimum necessary to achieve that aim.

The principle of proportionality obliges the Commission to resort to the least onerous measure when there is a choice between several appropriate measures, and the disadvantages caused must not be disproportionate to the aims pursued. This applies to requests for information or the choice of corrective measures to end an infringement. In the case of a financial penalty, the principle of proportionality requires the Commission to calculate the fine according to the gravity of the infringement and the degree of involvement of the undertaking concerned.