(See: Slave Laws Nullified)

Article I, Sec. II, Paragraph III: The Three-Fifths Clause (1787)
Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers, which shall be determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three-fifths of all other Persons.

Article I, Section IX, Clause I: The Importation Clause (1787)
The Migration or Importation of such Persons as any of the States now existing shall think proper to admit, shall not be prohibited by the Congress prior to the Year one thousand eight hundred and eight, but a Tax or duty may be imposed on such Importation, not exceeding ten dollars for each Person.

Article IV, Sec. II, Clause III: The Fugitive Slave Clause (1787)
No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, but shall be delivered up on Claim of the Party to whom such Service or Labour may be due.

The Dred Scott Decision
The March 6,1857, Dred Scott, US Supreme Court Decision rendering that chattel slaves, and said Negroes, including Freemen (non slave blacks) could never be citizens