In order to reach climate goals, governments need to gain support from their voters for the necessary policy interventions, such as carbon dioxide taxes. Previous research concludes that people often do not support and legitimize such taxes because they perceive them as unfair. However, the notion of fairness implies a multitude of factors and despite attempts of the previous research to further nuance people’s fairness perceptions, we currently lack a more precise understanding of what people mean when they regard carbon taxes as unfair. In this article, we thoroughly investigate this problem by using original survey data from YouGov collected in the United States in 2018 and analyzing open-ended survey responses on why people think carbon taxes are unfair. Applying structural topic modeling, we unpack the multi-dimensional meaning of unfairness, as perceived by the US population. The results from our analysis show that people regard carbon taxes based on gas pricing as unfair because they perceive gas prices already being high, because of the need to drive, unfairness for the poor or rural population, lack of trust in government, or considerations that the purpose of the tax is unjustified. These findings help provide a more nuanced policy design to address fairness concerns related to carbon taxes.