Article 191(2) of the Treaty on the Functioning of the European Union (TFEU) requires that Union policy be based on the principle that the polluter should pay and, on this basis, Directive 2003/87/EC provides for a transition to full auctioning over time.
Ceanglaítear le hAirteagal 191(2) den Chonradh ar Fheidhmiú an Aontais Eorpaigh (CFAE) go mbeidh beartas an Aontais bunaithe ar an bprionsabal a éilíonn gur cheart d'údar an truaillithe íoc as, agus, ar an mbonn sin, foráiltear le Treoir 2003/87/CE go n-aistreofar chuig ceantáil iomlán le himeacht ama.