NAFTA allows Americans to import cheap goods from Mexico without thoroughly inspecting the working conditions of the people who produce them. This is a very dangerous situation for human rights. Workers might not be protected under reasonable workplace conditions. NAFTA has made it easier for large companies to exploit workers from the developing world.
To an extent, NAFTA does uphold and advance human rights. Since NAFTA has gone into effect, trade between countries in the agreement has soared, allowing goods to be exchanged more frequently and cost-effectively. Still, the impact of labor provisions has been minimalized, so overall, I'd say this falls somewhere in the middle.