"The Act affects people's rights under the Bill of Rights Act and the committee should consider inviting the public to have input into the current review of the regime."
Orpin-Dowell used the example of an offender being subjected to a further period of supervision on an existing sentence.
"It's this additional punishment which can create an inconsistency between New Zealand offenders and overseas offenders," he said.
"The legislation may also apply retroactively. The Act applies to convictions in respect of offending which occurred before the Act was passed. This may be a direct breach of the prohibition against retroactive penalties in the Bill of Rights Act."
Orpin-Dowell said there are also "significant concerns" about how the Act is operating in practice, with special conditions appearing to be being imposed in all cases.
"This is inconsistent with the Attorney-General's expectations when the Act was passed and the Ministry of Justice's 2017 review report reveals the Act has not operated as intended," he added.
The Law Society has recommended special conditions only be imposed where the court is satisfied they are necessary to achieve the purposes of the Act.
It also recommended a range of other amendments, if the Act is to remain as part of New Zealand's laws.