Democratic presidential candidate Michael Bloomberg confirmed a report on Tuesday that calls on behalf of his campaign were being made by prison workers. He is seen here campaigning in Philadelphia on Saturday.

Billionaire presidential candidate Michael Bloomberg has acknowledged that one of his vendors hired a subcontractor that used prison workers to make phone calls for his 2020 campaign.

That prison labor was being used by the Bloomberg campaign was reported Thursday morning by The Intercept. The campaign says it was unaware that inmate workers were making phone calls on its behalf until informed by The Intercept’s reporter, and says it immediately cut ties to the vendor.

“Through a third-party vendor, the Mike Bloomberg 2020 campaign contracted New Jersey-based call center company ProCom, which runs calls centers in New Jersey and Oklahoma,” reporter John Washington writes. “Two of the call centers in Oklahoma are operated out of state prisons. In at least one of the two prisons, incarcerated people were contracted to make calls on behalf of the Bloomberg campaign.”

Sources told The Intercept that some of the calls were made by people incarcerated at the Dr. Eddie Warrior Correctional Center, a minimum-security women’s prison near Muskogee, Okla.

Bloomberg released a statement a few hours later in which he confirmed the reports:

Bloomberg is one of the world’s richest people, with a net worth estimated at about $56 billion. He built his wealth by founding his eponymous financial information and media company, and later was the mayor of New York City for 12 years.

He announced his candidacy for the Democratic nomination for president last month, and has already spent more than $76 million on television ads — far more than most of his Democratic rivals combined.