"There has been no significant decrease in the numbers of people detained on the mainland. In November 2018, there were 544 people who had been in detention more than one year - up from 505 in September, 2018."
"Worse, it is inexcusable that the numbers of people being held in detention longer than a year keeps growing. In November 2018, 281 people had been in detention over two years."
SBS News has contacted the Department of Home Affairs for a response to Mr Rintoul's claims.
Earlier Wednesday, the government announced two of the country's nine high-security immigration detention centres are being closed in what it said was a vindication of its border protection policy.
The Maribyrnong facility in Melbourne will close immediately after the last of the detainees there were moved to other centres on Monday.
The Blaxland centre, which is part of Villawood in Sydney, will close by May with the detainees also moved to the other seven centres.
There are 1250 people now in immigration detention in Australia. They are boat arrivals dating back to 2013 or earlier, people who have had their visas cancelled on character grounds and those who have overstayed their visas.
Immigration Minister David Coleman called it "another milestone in the ramping-down of Australia's onshore immigration detention network".
He said in a statement Labor's "catastrophic" border policy had forced the Rudd and Gillard governments to open 17 immigration detention facilities.
About 1000 people remain in immigration detention in offshore processing centres on Nauru and Manus, some have been there since 2013. The Christmas Island camp has been closed.
"The government has stopped the boats, got the children out of detention and closed the once-full immigration detention facilities," Mr Coleman said.
* Eight immigration detention centres remain in Australia, including Blaxland; there were 26 when Labor lost the election 2013
* 1250 held in total in these centres in 3 categories:
- boat arrivals dating back to 2013
- those with visas cancelled on character grounds, usually for committing crimes
- those who have overstayed their visas
* About 1000 remain on Nauru and Manus Island.