There was no Civil Rights Act in 1870 but in 1875, therefore I edited your question. However, please note that the 15th Amendment was ratified in 1870 which defines citizens' right to vote in section 1. In section 2 the amendment gives the Congress the power to enforce the amendment by further legislation. It is this part of the 15th Amendment that the 1875 Civil Rights Act was passed. This legislation gave the federal government the potential for increasing its control in state affairs. With this increased federal power there were subsequently several Supreme Court cases involving the Constitutionality of the 1875 Act. It was finally declared unconstitutional because it hindered implementation of the 14th Amendment which was ratified in 1868.