In cases T-339/16 Ville de Paris v Commission, T-352/16 Ville de Bruxelles v Commission and T-391/16 Ville de Madrid,1 the General Court held that cities have standing to challenge acts of the Commission that affect their regulatory powers. The effect was to allow Brussels, Paris, and Madrid to challenge Commission Regulation 2016/646 regarding emissions from light passenger and commercial vehicles.2 By way of background, Regulation 2016/646 introduced real driving emissions tests in order to prevent car manufacturers cheating emissions tests as they had done during the ‘dieselgate’ scandal. But the Regulation also watered down the more stringent Euro 6 emission limits for a transitional period (the so-called ‘conformity factor’). Paris, Brussels, and Madrid were aggrieved by the conformity factor and challenged the Regulation. Their concern was understandable given that the relaxation of the Euro 6 emission limits by way of the conformity factor was introduced by the Commission at the same time as France and Spain faced Commission infringement proceedings for persistently exceeding applicable limits of nitrogen dioxide and particulate matter.