If you are wondering what black codes are then I'll tell you. Black codes are laws limiting the rights of African Americans passed by southern governments.
Congress takes control
After johnson's plan barely making it by attacks from radical republicans congress is getting mad. Congress wants to take over reconstruction and not the president. President Johnson did not want to give up control of reconstruction. He also believed that some measures that congress passed were unnecessary so he vetoed them. In late 1866 the congressional elections gave the radical republicans two-thirds control of both houses of congress. With the power to override any veto, they launched their own reconstruction plan.