Democratic presidential candidate Michael Bloomberg admitted Tuesday after a report that his campaign unintentionally contracted with a service that used prison labor to help make calls for his campaign.

The Intercept reported that Bloomberg's campaign, through a third-party vendor, contracted with a New Jersey-based call center ProCom that, in part, used prison labor. In at least one instance, The Intercept reported, Oklahoma inmates were used to make calls on behalf of the New York City billionaire's campaign.

NBC News has not independently verified The Intercept's reporting, which is not disputed by the Bloomberg campaign.

"We only learned about this when the reporter called us," Bloomberg wrote in a statement released by his campaign, "but as soon as we discovered which vendor's subcontractor had done this, we immediately ended our relationship with the company and the people who hired them."

"We do not support this practice and we are making sure our vendors more properly vet their subcontractors moving forward," he continued.

Bloomberg spokesperson Julie Wood provided a similar statement to The Intercept.

Bloomberg's candidacy was already under fire from criminal justice reform advocates, who have been skeptical of the former mayor's defense of the controversial policing policy known as "stop and frisk."

In 2013, a federal judge ruled the practice unconstitutional, saying it amounted to "indirect racial profiling” that singled out black and Hispanic men. Ahead of his late entry into the 2020 field, Bloomberg apologized for the policy while addressing a black church, saying he can't change history but "I want you to know that I realize back then I was wrong."