More than 150 years after slaves were freed in the U.S., voters in five states will soon decide whether to close loopholes that led to the proliferation of a different form of slavery — forced labor by people convicted of certain crimes. None of the proposals would force immediate changes inside the states' prisons, though they could lead to legal challenges related to how they use prison labor, a lasting imprint of slavery’s legacy on the entire United States. The effort is part of a national push to amend the 13th Amendment to the U.S. Constitution that banned enslavement or involuntary servitude except as a form of criminal punishment.