Minister Keenan has slammed the Federal Opposition in a statement overnight, saying its stance would "allow more paedophiles into the community".
"The Coalition Government's proposed reforms would be the toughest crackdown on child sex offenders in a generation but Labor has put children across the nation at risk by opposing mandatory minimum sentences for these heinous crimes," Mr Keenan said.
Current laws weren't tough enough, he said, citing figures that showed more than 40 per cent of child sex offenders convicted under federal laws since 2012 escaped jail time.
"For those who did, the most common period of actual imprisonment was just six months. This is not acceptable," he said.
Mr Keenan said predators "may not even spend one day behind bars" if Labor blocked the new laws.
Labor will back all of the measures in the government's bill before parliament except for the compulsory jail terms.
The party claims the laws would potentially lead to teenagers being locked up for five years for a consensual relationships with teens only a few years younger.
It could also lead to child sex offenders escaping any jail time.
"Mandatory minimums let guilty people off the hook because juries are less likely to convict them when they know there is no discretion about the sentence," Labor's Justice spokeswoman Clare O'Neil told parliament.
She also said mandatory sentences would mean criminals wouldn't co-operate with police to give up the "kingpins" of paedophile networks if they knew they would be locked up anyway.
"I don't want to put people away for five years - I want to catch the kingpins who are the drivers of this disgusting behaviour and I want judges to be able to put them away for life," Ms O'Neil said.
She also said teenagers should not be locked up for five years for sharing sexual images over Snapchat.
"The Law Council points out that this behaviour between a 15-year-old and a 17-year-old in a consensual relationship is perfectly legal," she said.
"On the day the older person turns 18, suddenly that person has committed a range of federal offences and will go to jail for a minimum of five years.
"These are crimes. A consensual sexual relationship between a 15-year-old and an 18-year-old is a crime; I don't devalue that.
"But does the Minister for Justice really believe that the young people in this relationship belong in jail for five years?"
Labor also proposed other tougher amendments to the law, including life jail terms for aggravated sex offenders, increasing the maximum sentences for the most serious child sex crimes by five years, to 20 and 25 years imprisonment, and tougher penalties for paedophiles who travel overseas to abuse children.
The ringleaders of child abuse networks would also face penalties, under Labor's amendments.
"They facilitate the production and distribution of sometimes sadistic and brutal material, and courts must be able to punish them appropriately," Ms O'Neil said.
Mr Keenan argued for the mandatory terms however, saying the government's child sex offender reforms were based on advice from Australia's law enforcement agencies.
"A vote against these reforms is a vote to allow more paedophiles into the community," he said.
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