Judgment of the Court (Sixth Chamber) of 13 March 2019.#Republic of Poland v European Parliament and Council of the European Union.#Action for annulment — Directive (EU) 2016/2284 — Reduction of national emissions of certain atmospheric pollutants — Adoption of EU legal acts — Course of the legislative procedure — Article 4(3) TEU — Principle of sincere cooperation — Actual exercise of the EU legislature’s discretion — Impact assessment — Sufficient assessment of the effects of the contested measure — Article 5(4) TEU — Principle of proportionality — Article 4(2) TEU — Equality of Member States before the Treaties — Article 191(2) TFEU — Environmental policy of the European Union — Consideration of the diversity of the regions of the European Union — Judicial review.#Case C-128/17.