Mike Bloomberg's campaign used prison labor to make campaign calls for the former mayor's 2020 presidential bid, according to an investigation by The Intercept.

Why it matters: Scrutiny on Bloomberg's self-financed campaign has increased since jumping in the race and spending more than $100 million. The latest polling has Bloomberg leading the lower-tier candidates, just behind Mayor Pete Buttigieg.

The big picture: The campaign contracted the company ProCom, which runs calls centers in New Jersey and Oklahoma, to make campaign calls. Two of the company's call centers in Oklahoma are in state prisons.

Incarcerated people in one of the prisons made calls to voters in California on behalf of the campaign, a source, who asked for anonymity, told The Intercept.

What they're saying: The Bloomberg campaign confirmed the contract in a statement to The Intercept, saying “We didn’t know about this and we never would have allowed it if we had. We don’t believe in this practice and we’ve now ended our relationship with the subcontractor in question.”

The campaign said it has asked vendors to vet subcontractors more closely in the future.

Of note: A ProCom co-founder said the company pays its inmates Oklahoma's minimum wage of $7.25 an hour through the the Oklahoma Department of Corrections.

The state's department of corrections website lists the maximum monthly wage for incarcerated people at $20 dollars a month. Another policy document says the incarcerated may receive a maximum pay of $27.09 per month.

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