“Prison labor is slave labor. Pass the #AbolitionAmendment.”

Congressional Democrats on Monday marked the 156th anniversary of the ratification of the 13th Amendment to the U.S. Constitution by calling on federal lawmakers to end a form of slavery that has been allowed to persist in the United States.

“Abolishing slavery can’t come with a loophole.”

Passed by Congress in January 1865 and ratified by the requisite number of states in the wake of the U.S. Civil War, the 13th Amendment outlawed slavery and involuntary servitude “except as a punishment for crime whereof the party shall have been duly convicted.”

Leading up to Juneteenth earlier this year, U.S. Sen. Jeff Merkley (D-Ore.) and Rep. Nikema Williams (D-Ga.) reintroduced the Abolition Amendment—which, as they put it, would “close the slavery loophole” by overriding that clause in the 13th Amendment.

Since the amendment was ratified in December 1865, “that sinister loophole has driven discriminatory policing and mass incarceration,” Merkley noted Monday. “Abolishing slavery can’t come with a loophole.”

Williams similarly pointed out that “prisons disproportionately exploit the labor of Black and Brown folks for profit, while stripping them of their individuality and liberty.”

“Prison labor is slave labor. Pass the #AbolitionAmendment,” she tweeted, urging fellow lawmakers to #EndTheException.

Supporters of the Abolition Amendment also used those hashtags to draw attention to the proposal on social media Monday.

“As long as prison labor continues to exist, slavery will persist in America,” said Rep. Yvette Clarke (D-N.Y.). “Today, 156 years after our nation ratified the 13th Amendment, it is long past time we take what it stands for seriously. Enough is enough.”

Others who highlighted the proposal on Monday include Reps. André Carson (D-Ind.), Troy Carter (D-La.), Adriano Espaillat (D-N.Y.), Hank Johnson (D-Ga.), Dutch Ruppersberger (D-Md.), Bobby Rush (D-Ill.), Ritchie Torres (D-N.Y.), Frederica Wilson (D-Fla.), and Marc Veasey (D-Texas).

Along with several Democratic lawmakers in the U.S. Senate and House of Representatives, the Abolition Amendment is supported by dozens of human rights groups.

Two-thirds of each chamber of Congress would have to vote for the proposal, then three-quarters of state legislatures would need to ratify it, for the amendment to take effect.

This post has been updated with additional details about the ratification of the 13th Amendment.