Why would white southerners pass laws that controlled the movement of african americans?

White southerners would pass laws that controlled the movement of African-Americans because African-Americans were a large part of their workforce. This was especially true during ther era of Reconstruction. If a large amount of African-Americans moved away from the South, it would decrease the amount of workers available to work on farms on plantations. If there were less workers, that means farmers/plantation owners would make less products, reducing the amount of profit they could make.