R. v. K.R.J., 2016 SCC 31:
Section 11 (i) of the Charter constitutionally enshrines the fundamental notion that criminal laws should generally not operate retrospectively. This constitutional aversion for retrospective criminal laws is primarily motivated by the desire to protect the fairness of criminal proceedings and safeguard the rule of law. Rules pertaining to criminal punishment should be clear and certain. To attract the protection of s. 11 (i), the new prohibition measures must qualify as “punishment”. In R. v. Rodgers, 2006 SCC 15,  1 S.C.R. 554, this Court developed a two‑part test for determining whether a consequence amounts to punishment under s. 11 (i): (1) the measure must be a consequence of a conviction that forms part of the arsenal of sanctions to which an accused may be liable in respect of a particular offence; and (2) it must be imposed in furtherance of the purpose and principles of sentencing.
This test requires two clarifications. First, while not all measures imposed to protect the public constitute punishment, public protection is at the core of the purpose and principles of sentencing and is therefore an insufficient litmus test for defining punishment. Thus, sanctions intended to advance public safety do not constitute a broad exception to the protection s. 11 (i) affords and may qualify as punishment. Second, the s. 11 (i) test for punishment must embody a clearer, more meaningful consideration of the impact a sanction can have on an offender. Doing so enhances fairness and predictability in punishment and is consistent with this Court’s jurisprudence.
Accordingly, the s. 11 (i) test for punishment should be restated as follows: a measure constitutes punishment if (1) it is a consequence of conviction that forms part of the arsenal of sanctions to which an accused may be liable in respect of a particular offence, and either (2) it is imposed in furtherance of the purpose and principles of sentencing, or (3) it has a significant impact on an offender’s liberty or security interests. To satisfy the third branch of this test, a consequence of conviction must significantly constrain a person’s ability to engage in otherwise lawful conduct or impose significant burdens not imposed on other members of the public.