US presidential hopeful blames contractor after report reveals prison inmates made phone calls on his behalf.

Billionaire US presidential candidate Michael Bloomberg has admitted that his campaign used prison labour to push out his 2020 message to voters by phone.

The former mayor of New York, who last month entered the Democratic Party race to face Republican President Donald Trump in the November 2020 election, said in a statement on Tuesday that his team had not been aware of the cold call arrangement until Monday.

“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,” Bloomberg said.

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

Earlier today, a news outlet accurately reported that a subcontractor for one of our vendors was using prison workers to make phone calls on behalf of my campaign. After learning this, we immediately ended our relationship with that company. Full statement below: pic.twitter.com/0KJ8y8Iqxj — Mike Bloomberg (@MikeBloomberg) December 24, 2019

Bloomberg’s mea culpa came after The Intercept reported the Bloomberg campaign had hired a telecommunications company called ProCom, which runs call centres in New Jersey and Oklahoma.

Two of the company’s Oklahoma call centres are operating out of state prisons. One of those call centres was involved in the Bloomberg campaign push, meaning inmates were making calls on the former mayor’s behalf.

The Oklahoma Department of Corrections website states that inmates in the state can only make a maximum of $20 per month for “institutional jobs”.

Have you been contacted recently by @MikeBloomberg’s 2020 presidential campaign? Well, most likely, you were talking to a criminal in a prison he contracted to make calls on his campaign’s behalf. #wow https://t.co/MI06GtDG0d — NRA (@NRA) December 24, 2019

The prison labour blunder comes as Bloomberg has seen some positive 2020 news.

Despite joining the race late, he placed fifth in several recent polls, behind primary front-runners Joe Biden, Elizabeth Warren, Bernie Sanders and Pete Buttigieg.

A Reuters/Ipsos opinion poll conducted on December 18-19 showed that about 5 percent of Democratic-leaning voters support Bloomberg.

That is despite having not qualified for a single debate yet.

Ranked by Forbes as the eighth-richest American, Bloomberg has spent more on campaign ads in the last few weeks than his main Democratic rivals have all year.

Bloomberg plans to skip the first four primary elections next year in favour of spending all of his energy on the Super Tuesday contests.