More than 150 years after the ratification of the US Constitution’s 13th Amendment, Colorado has officially abolished slavery. Coloradans voted Tuesday for Amendment A, a measure removing language in the state constitution that allowed prison labor without pay.

Colorado is one of more than a dozen states whose state constitution technically still allows involuntary servitude as a form of criminal punishment. The state’s language closely resembles a contested passage that remains in the US Constitution 13th Amendment, which outlawed chattel slavery, but allowed those convicted of crimes to be forced into labor.

This is what that language looks like in the 13th Amendment (emphasis added):

Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction

And this is what the language looked like in Colorado’s state constitution before voters backed Amendment A (again, emphasis added):

There shall never be in this state either slavery or involuntary servitude, except as a punishment for crime, whereof the party shall have been duly convicted.

The previous language was strongly opposed by local activists like Jumoke Emery, a lead organizer with Abolish Slavery Colorado, one of the groups that has worked alongside the state ACLU and NAACP to build support for the new amendment.

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“I hope that this puts forth the message that our past doesn’t have to be our future, that by and large we as Americans are interested in fixing our mistakes,” Emery told CNN last month when discussing the amendment. Amendment A was sponsored in the Colorado state legislature by three Democrats, Rep. Jovan Melton, Rep. Joseph Salazar, and Sen. Angela Williams, and one Republican Sen. Larry Crowder.

Similar language in the 13th Amendment, which is alternatively referred to as the “exception clause” or the “punishment clause,” has been criticized by those affiliated with movements like the National Prison Strike.

The Tuesday result makes Colorado one of the first states to remove this language from its constitution. Governing magazine notes that bills “with similar goals failed this year in Wisconsin and stalled in Tennessee.”

But this wasn’t the first time that such a proposal has appeared on Colorado ballots. In 2016, with the backing of state politicians and various local advocacy groups, a similar measure called Amendment T aimed to remove the “slavery as punishment” language from the state constitution. But the amendment was rejected by the state’s voters, a development experts like University of Colorado Law professor Melissa Hart blamed less on overt racism and more on the confusing way the amendment was written.

After failing in 2016, Colorado activists mounted a new campaign to remove the slavery language

With the amendment on the ballot for a second time in 2018, advocates argued that the state had a second chance to officially abolish prison slavery. A number of groups and officials weighed in on the measure earlier this year before it was added to the ballot.

“We did our due diligence ahead of time, and we had legal assistance from the state legislature, from the ACLU,” Emery told the Colorado Independent last month.

Supporters of the measure largely focused on simplifying how the amendment was worded on ballots in an effort to avoid this highly confusing question from 2016:

Shall there be an amendment to the Colorado Constitution concerning the removal of the exception to the prohibition of slavery and involuntary servitude when used as a punishment for persons duly convicted of a crime?

At the time, supporters of the measure argued that this question was simply too convoluted for voters, and nearly 300,000 voters skipped the question when filling out their ballots two years ago.

“I don’t think this was a pushback at all by individuals saying they wanted slavery in the Constitution,” Rep. Joe Salazar, a Democrat who sponsored legislation to get Amendment T on the 2016 ballot, told the New York Times. “I just think the language was too confusing.” In addition to Salazar, Amendment T was also sponsored by state Democrats Sen. Jessie Ulibarri and Rep. Jovan Melton.

In 2018, the ballot question was changed to be clearer, and much like two years prior, the proposal enjoyed unanimous support from Colorado state legislators and local advocacy groups. The measure received very little public opposition, and no groups mounted an organized challenge to the amendment.

However, Amendment A did face some criticism. In an October article in the Colorado Independent, Dan Rubinstein, a Republican district attorney representing Mesa County, argued that the amendment called unnecessary attention to a settled issue, and that removing the slavery language was redundant. He added that the amendment would effectively ban community-service punishments and have the unintended consequence of increasing the number of people incarcerated or those subject to significant fines.

That argument was swiftly challenged by other local experts. “This amendment has a pretty clear reading, and I really don’t see it causing the mischief that some are worried about,” University of Colorado law professor Phil Weiser told the Independent.

While official opposition to the amendment has been limited, activists promoting Amendment A have been subjected to harassment. On Monday, Emery a posted a photo of a pile of burned Amendment A flyers on Facebook, saying that the flyers had been burned on his front porch. In an interview with the Colorado Sun, Emery likened the action to “a cross burning in my front yard.”

In the run-up to the election, there was also some confusion due to the state’s voting guide, also known as a Blue Book, which is given to voters shortly before they cast their ballots. The book is required to include arguments for and against each proposed amendment, and noted that voting yes to remove the language “makes an important symbolic statement,” adding that the 25 states who currently do not have any language about slavery in their constitutions still have prison work and community service programs.

But the book also noted that the amendment “can be viewed as making a change to the Colorado constitution that is redundant,” wording that might lead some people to vote no.

With the amendment passing successfully this time, advocates finally achieved the victory they fought for two years ago. But they acknowledge that this victory is more about the reaffirming the state’s values than immediately changing prison labor conditions.

“This won’t have a direct impact on prison reform or how inmates are treated,” Kamau Allen, an organizer with Abolish Slavery Colorado, told Fox News in July. “But it is definitely more impactful than removing something like a Confederate monument, because this will actually change the text of a living document.”