CSA Constitution is really explicit
Section 9 - Limits on Congress, Bill of Rights
1. The importation of negroes of the African race from any foreign country other than the slaveholding States or Territories of the United States of America, is hereby forbidden; and Congress is required to pass such laws as shall effectually prevent the same.
2. Congress shall also have power to prohibit the introduction of slaves from any State not a member of, or Territory not belonging to, this Confederacy.
4. No bill of attainder, ex post facto law, or law denying or impairing the right of property in negro slaves shall be passed.