Omega 事件（Case C-27/00 and C-122/00, Omega [2002] ECR I-2569）において、WTO諸協定やその他の国際条約よりも厳格な環境保護基準を導入するEC法は、比例性の原則 に反するため、無効かという問題が提起されたが、EC裁判所は、立法機関（EU理事会）には広範な裁量権が与えられていることを確認した上で、その判断が明らかに誤りであるとは言えないとし、比例性の原則に違反するものではないと述べている（paras. 62-74）。したがって、WTO諸協定よりも厳格な保護基準を導入することも適法と解される。EC裁判所の判断（先行判断）は以下の通りである。
　

62 On this point, it should be remembered that it is settled case-law that the principle of proportionality, which is one of the general principles of Community law, requires that measures adopted by Community institutions should not exceed the limits of what is appropriate and necessary in order to attain the objectives pursued by the legislation in question, and where there is a choice between several appropriate measures, recourse must be had to the least onerous, and the disadvantages caused must not be disproportionate to the aims pursued (see, in particular, Case C-331/88 Fedesa and Others [1990] ECR I-4023, paragraph 13, Case C-180/96 United Kingdom v Commission, cited above, paragraph 96, and Case C-101/98 UDL [1999] ECR I-8841, paragraph 30).

63 It is also settled case-law, with respect to judicial review of the conditions mentioned in the preceding paragraph, that the Community legislature has wide legislative powers in the field of the common transport policy as regards the adoption of appropriate common rules (see, to that effect, in particular, Joined Cases C-248/95 and C-249/95 SAM Schiffahrt and Stapf [1997] ECR I-4475, paragraph 23).

64 In reviewing the exercise of such powers, the Court cannot substitute its own assessment for that of the Community legislature, but must confine itself to examining whether that latter assessment contains a manifest error or constitutes a misuse of powers or whether the authority in question clearly exceeded the bounds of its discretion (see, in particular, SAM Schiffahrt and Stapf, paragraph 24).

65 Moreover, the Court's case-law also shows that where, as in this case, implementation by the Council of a common policy requires it to assess a complex economic situation, its discretion is exercisable not only in relation to the nature and scope of the provisions which are to be adopted but also, to a certain extent, to the findings as to the basic facts, especially in the sense that it is free to base its assessment, if necessary, on findings of a general nature (see, in particular, SAM Schiffahrt and Stapf, paragraph 25).

66 In the present case, the Council did not exceed its margin of appreciation in taking the view that the criterion of a by-pass ratio of 3 or more could contribute to the objective of reducing the damage to the environment caused by air traffic in terms of noise, fuel burn and gaseous emissions.

67 Nor has Omega shown that the criterion relating to by-pass ratio was inappropriate.

68 Moreover, its assertions, which are in any case disputed by the United Kingdom Government, refer exclusively to a particular type of aeroplane, the projected re-engined Boeing 707s. These assertions are no more than forecasts, since those aeroplanes have not yet undergone certification tests, as the Advocate General has observed in point 76 of his Opinion.

69 The Commission, on the other hand, has produced general data on the development of noise pollution and fuel burn of aeroplanes over the three decades from the 1960s to the beginning of the 1990s. Those data show that the gradual increase in by-pass ratios during that period was accompanied by a reduction of noise emissions by 20 to 25 EPNdB, which is equivalent to a four- to five-fold reduction in perceived noise nuisance, and to a reduction in fuel consumption per passenger on long-haul flights by over 50%, with a consequent reduction in gaseous emissions.

70 Moreover, the Community legislature has already in the past enacted other legislation based on the criterion that a higher by-pass ratio is an indication that the engine is less noisy. A by-pass ratio of 2 is used in Article 4(e) of Directive 89/629 (see paragraph 24 above) and Article 2(1) of Directive 92/14 (see paragraph 26 above) as an alternative to compliance with the Chapter 3 noise standards. That alternative is also suggested in Resolutions A31-11 and A32-8 of the ICAO Assembly recommending the Member States to introduce a derogation for aeroplanes with engines with a high by-pass ratio in the event of early application of the Chapter 3 thresholds (see paragraph 19 above).

71 Omega further submits that alternative measures could have been adopted which would have been economically less damaging for it, and that aircraft noise can come from sources other than the engines.

72 On this point, even if such measures could make a sufficient contribution to reducing environmental damage caused by air traffic, the Council could reasonably take into consideration that the application of separate criteria relating to the reduction of noise, fuel burn and gaseous emissions would have represented a highly complex operation which was not justified by the limited number of aeroplanes such as those re-engined by Omega. In the same way, it could reasonably consider that reference to a single technical criterion could remove the uncertainties which specific standards might allow to persist. Thus, for the problem of noise alone, if the take-off, landing and sideline figures had to be weighted, the question could also arise whether the differentiated influence of noise volumes ought not to be taken into account. For those reasons, the Council did not commit a manifest error of assessment in its choice of criteria by taking account of the fact that the by-pass ratio appears more workable because it requires fewer tests and measurements, both in terms of design and control.

73 In those circumstances, it does not appear that the Council committed a manifest error of assessment by considering it necessary to authorise the re-engining of aeroplanes only using engines with a by-pass ratio of 3 or more.

74 Accordingly, it does not appear that Article 2(2) of the Regulation infringes the principle of proportionality.