The “green taxation,” which usually includes taxes on energy, transport, pollution, and resources, is being used to achieve environmental and sustainability purposes. The European Union is promoting this strategy, creating different provisions related to the usage of taxes to change environmental behaviors. Portugal, as a member-estate of European Union, follows this path establishing a policy where taxes are being used for these purposes. However, “green taxation” is also a significant form of revenue and, currently, it is difficult to define the criteria for the creation of these taxes, as they are not considering the ability to pay (one of the main principles in the creation of taxes) affecting the equitable distribution of the tax burden. The authors can conclude that, with the masking of “taxes required for environmental protection,” these taxes are being used as an additional source of revenue, distorting the principles underlying the creation and collection of taxes.