LINCOLN, Neb. (AP) – A Nebraska lawmaker is looking to close a 143-year-old loophole in the state constitution that allows people to be enslaved as punishment for a crime.

Sen. Justin Wayne, of Omaha, says he will introduce a ballot proposal to amend the constitution during the legislative session that begins Wednesday.

The Nebraska Constitution has banned slavery and involuntary servitude since 1875, except as punishment for a crime. Wayne says the loophole was used to force former slaves back into unpaid labor for private parties, a system known as convict leasing.

Wayne says the state constitution serves as the moral and legal foundation for Nebraska’s laws, and removing the language shows slavery is not a Nebraska value.

The measure would need approval from the Legislature and voters to go into effect.