The PIS tax is considered by the majority doctrine as a contribution due to Social Security. There was judicial discussion about the real legal nature of this tax, as well as about the legitimacy of its collection from social assistance entities, since they should enjoy the immunity provided for in § 7 of article 195 of the Federal Constitution. The present study through doctrinal and jurisprudential analysis comes to ascertain what would be the real legal nature of the tax and what is the nature of the regulatory standard of the requirements for the enjoyment of such immunity. The survey shows that the PIS is a tax due to social security, since, at present, its purpose is to collect unemployment insurance and salary allowance, elements of social security. It was also proven that the Federal Supreme Court understands that both ordinary law and complementary law can be used to configure the requirements to be met by social assistance entities to enjoy such constitutional benefit.