It's believed taxpayers could save millions of dollars if foreign prisoners were deported instantly.
As of December 2017, 242 inmates who were earmarked for deportation were serving time in New Zealand prisons.
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Newshub can reveal those prisoners will cost taxpayers more than $200 million by the time they are all released.
South African-born psychiatrist Colin Bouwer served 17 years for the murder of his wife in 1999. Using today's figures, it would have cost $1.8m to keep him locked up before he was deported in October 2017.
Sensible Sentencing Trust founder Garth McVicar says there's no room for criminals like Bouwer.
"It is an obvious solution," he told Newshub. "We get rid of 240-odd, 250 inmates, we reduce their cost by $30 million."
However the father of murder victim Renee Duckmanton says he's happy to pay for his daughter's killer to remain behind bars rather than be deported.
Ms Duckmanton was killed by Gambian-born Sainey Marong in 2016. He's one of the 242 prisoners with an active deportation alert.
Her father Brent McGrath told Newshub he wants to make sure Marong and criminals like him serve their time.
"Even though I'm paying for it as a taxpayer, I think they should do their time here."