2019-09-022019-09-022019-09-022019-06https://ri.ucsal.br/handle/prefix/951The present article has as object of discussion the unconstitutionality applied to the collection of the differential of ICMS rates of Micro and Small Enterprises opting for National Simples. The SIMPLE institute was created to simplify the collection of the taxes destined to these companies, since they are more fragile and, consequently, they lack a more subtle regime, since at present the ME and EPP are of great relevance for the economy national. It was sought to bring the essence of the Brazilian tax system from the origin so that it would then deepen on the dealings given to the tax in question, as well as the relevant aspects of its composition. However, as will be approached in the course of the present work, with the normalization of Constitutional Amendment No. 87/2015, which brought with it the application of the Aliquot Differential regime for cases related to ICMS, which, although not affecting the companies opting for the Simple, it opened the doors for the Ministry of Finance to establish ICMS 93 Agreement, of 2015, and with it the application of the Micro and Small Companies, which will be demonstrated during the present study, a flawed conduct of unconstitutionality.Acesso AbertoSistema tributárioICMSSimples NacionalDifalInconstitucionalidadeTax systemICMSSimple nationalUnconstitutionalityTrabalho de Conclusão de CursoCiências Sociais AplicadasDireito