Prisoners' mail looks set to be more tightly controlled, including being blocked if its message could go viral online or if it could be harmful to groups of people based on race, religious beliefs, sexual orientation or political opinion.
And prison managers will also be able to consider coded language - which appears to be harmless but is commonly used by extremist groups - in determining whether to withhold a prisoner's mail.
Corrections Minister Kelvin Davis has added the new rules to the Corrections Amendment Bill, which will have its third reading tomorrow and is expected to pass with the support of Labour, New Zealand First and the Greens.
The new provisions will add new restrictions on the right to freedom of expression, but the Davis said they were justified.
The changes follow a review of whether the law was fit for purpose after the failure of Corrections to properly vet the mail sent from prison by the accused March 15 gunman.
In August, a letter from the accused that Corrections should have withheld was published on the 4chan website, and Corrections later revealed that a second letter from the accused was mistakenly let through the system.
Despite putting these mistakes down to human error and implementing tighter rules for the accused's mail, Davis ordered a review of the law.
The law already allows prisoners' mail to be blocked for a number of reasons including whether it might threaten or intimidate the recipient, endanger the safety or welfare of someone, or encourage an offence.
The new rules would:
• lower the threshold of what mail might be harmful by considering both direct and indirect effects, which would include someone seeing it on social media
• take account of whether the mail might threaten or intimidate not only the mail's recipient, but any person
• add discrimination as new grounds for blocking mail as per the Human Rights Act, which includes race, religious belief, sexual orientation, sex, marital status, disability, age, political opinion and employment status.
Prison managers will also consider "the potential for messages to be disseminated through coded references".
Online hate speech is often expressed in coded language in an attempt to avoid being flagged as harmful content.
Certain numbers are used to reference Adolf Hitler, "RAHOWA" is used for "racial holy war", and "ZOG" or "JOG" relate to Zionist or Jewish conspiracy theories.
Other examples include "Stacey", used to mean an attractive woman who is only interested in attractive men, or "snowflake", a derogatory term used to describe left-wingers.
Davis said that a group of experts would advise prison managers on what might be coded language and potentially grounds for withholding mail.
Advice to the Government said the current law was at risk of being exploited by prisoners seeking to radicalise or re-victimise people, or promote hostility against groups such as those based on race or religious beliefs.
Corrections could block this type of mail without changing the law, but it would be open to legal challenge and possible compensation payments to the inmates who had written the letters.
In its regulatory impact statement (RIS) on the changes, the Treasury said that Corrections would be able to withhold harmful mail that could be posted online and widely shared.
"These individuals may also become a focal point for sympathetic individuals and groups in the community, who may seek to draw attention to and amplify their hostile views," Treasury's RIS said.
Using racism as grounds for blocking prisoner mail is already possible under the current law, but existing case law meant that the bar was set high to justify restricting one's right to freedom of expression.
The current law also excludes discrimination based on anything other than race as grounds for a civil offence.
Amending the law so that prisoner mail could only be sent if it supported prisoner rehabilitation was also considered, but rejected as it could easily be circumvented or applied too widely.
The changes do not include the words "extremism" or "violent extremism", which aligns with Ministry of Justice advice that those terms were open to interpretation.
The changes were introduced to the Corrections Amendment bill last week during the bill's committee of the whole House stage, and were supported by Labour, NZ First and the Greens, but opposed by National.
National's objections to the bill were less about the bill's changes to prisoners' mail and more about the use of police cells to house prisoners, which National supports.