Breivik's lawyer Tord Jordet told Aftenposten newspaper that the long period of isolation his client had endured constituted an additional punishment, which had not been part of the 21-year sentence he received in 2012.
"We're looking into it now, and after the summer holiday we will make the decision as to whether we will do it or not," Breivik's lawyer Geir Lippestad told The Local. "At some point, it will be against human rights, so the prison must have a plan to rehabilitate him and those plans don't exist today."
The 35-year-old, who killed 77 people in a twin bomb and gun massacre in the summer of 2011, has been kept in "especially high security" in the Ila and Skien prisons since.
Breivik's plea could reopen one of the key questions raised in his trial in 2012 — the extent to which the network of anti-Islamic militants he claimed he belonged to were simply a fantasy he had concocted.
Norwegian law allows prisons to impose "especially high security" on prisoners who pose a "special risk of escape", who might receive "external assistance to escape", or who might take hostages or carry out further dangerous crimes.
Lippestad said he did not believe that there was anything special about Breivik that put him at a higher risk of escape.
"There are a lot of different people in prison and I don't think it's more dangerous for him than anyone than for anyone else," he said. "He's in a maximum security reason and there's no way he can get out."
Harald Stabell, one of Norway's most prominent defenders, argued that the time Breivik had spent in isolation was unacceptable.
"His case is undoubtedly special, thankfully, but it still does not justify this isolation regime," he said. "There must be other ways to reduce the risk of escape, while maintaining his own safety."
Police in Norway in February closed a preliminary investigation into Breivik's complaints that his prison conditions amounted to "serious torture".
Breivik in January 2013 filed a formal complaint against Norway's minister of justice and the director of Ila prison.
In the complaint, Breivik lamented the lack of activities on offer, countless body searches and an "almost total" ban on expressing himself – all of which, according to his lawyer, violate Norway's law that prohibits acts of "aggravated torture".