With the growing awareness among entrepreneurs and consumers within the tourism industry regarding the field of sustainable development, it seems necessary to base hotel classification systems on an integrated approach to management quality, including the fulfillment of ecological and environmental criteria. However, this topic has yet to be recognized in the literature, especially concerning the European market. Therefore, this article aims to fill this research gap and indicate how environmental standards have been implemented in the European system of hotel classification—Hotelstars Union (HSU)—and that in force in Poland. With regard to these systems, the differences in the classification criteria taken into account by the certifying organizations in the European Union (EU) and the administrative hotel categorization system in Poland are pointed out. Particular emphasis is placed on the criteria related to environmental management in the hotel industry. The criteria related to environmental management were identified through an analysis of the criteria of eight environmental management systems that are applicable to the contemporary hotel industry. The results of this research prove that, even though the HSU system takes the principles of sustainable development into account to a much greater extent than the Polish system, its primary weakness is that most of its criteria related to the environment are optional. In addition, the optional criteria have higher weights than the obligatory ones. In turn, the Polish classification system makes very little reference to environmental standards. Moreover, it is not detailed, and the assessment criteria are not up to date. Therefore, it is recommended that a greater number of environmental criteria be included in the next update of the HSU system, which should be obligatory for hotels to meet. In addition, the sustainability criteria included in the HSU system should be adapted to the policy system aimed at the hotel industry in Poland and other EU countries.