The Court (Grand Chamber) :

1. Sets aside the judgment of the General Court of the European Union of 4 December 2018, Carreras Sequeros and Others v Commission (T‑518/16, EU:T:2018:873);
2. Dismisses the action brought by Mr Francisco Carreras Sequeros, Ms Mariola de las Heras Ojeda, Mr Olivier Maes, Mr Gabrio Marinozzi, Mr Giacomo Miserocchi and Mr Marc Thieme Groen in Case T‑518/16;
3. Orders Mr Francisco Carreras Sequeros, Ms Mariola de las Heras Ojeda, Mr Olivier Maes, Mr Gabrio Marinozzi, Mr Giacomo Miserocchi and Mr Marc Thieme Groen to bear their own costs and to pay those incurred by the Council of the European Union in the context of the present appeals and of the proceedings before the General Court of the European Union, as well as those incurred by the European Commission in the context of the latter proceedings;
4. Orders the Commission to bear its own costs incurred in the context of the present appeals;
5. Orders the European Parliament to bear its own costs.