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They enacted a series of restrictive laws known as "black codes," which were designed to restrict freed blacks' activity and ensure their availability as a labor force now that slavery had been abolished. For instance, many states required blacks to sign yearly labor contracts; if they refused, they risked being arrested as vagrants and fined or forced into unpaid labor.
What is Northern outrage over the black codes helped undermine support for Johnson's policies, and by late 1866 control over Reconstruction had shifted to the more radical wing of the Republican Party in Congress.