An increasing number of tax jurisdictions are implementing the concept of cooperative compliance into their tax systems. It aims to improve tax compliance by building an enhanced relationship between tax authorities and taxpayers. In principle, the programme is aimed at large taxpayers capable of engaging in aggressive tax optimization that is detrimental to state revenue. Dedicating the programme exclusively to large taxpayers may raise doubts about whether it violates the principle of equality before the law. In Poland, the legislation governing the cooperative compliance programme was introduced on July 1, 2020. As in other countries, it was targeted at large taxpayers. The article therefore discusses the question whether the Polish legal regulations on cooperative tax compliance are in line with the constitutional principle of equality.