Constitutional cases usually have implications that go beyond the immediate dispute between the parties. Appeals in such cases thus frequently attract the interest of interveners. But when can an intervener truly add a new perspective? And when should a proposed intervention be denied because the intervener is allegedly raising a new issue, thereby prejudicing other parties? The Ontario Court of Appeal’s February 28, 2014 decision in P.S. v. Ontario considered these issues. It demonstrates that courts are inclined to hear different viewpoints in constitutional cases, and unless a proposed intervener’s submissions would be truly repetitive or would raise entirely new issues that would prejudice other parties, motions to intervene in such cases will usually be granted.
The case involves an individual, Mr. S, who has been detained in Waypoint Centre for Mental Health Care (“Waypoint”) since 1996. He brought an application alleging that Waypoint violated his rights under various sections of the Canadian Charter of Rights and Freedoms (“Charter”). His application was largely dismissed in the Superior Court. The Canadian Civil Liberties Association (“CCLA”) and the Mental Health Legal Committee (“MHLC”) sought leave to intervene as friends of the Court on appeal. Mr. S supported the intervention motions but Waypoint, as well as the Attorneys General of Canada (“AG Canada”) and Ontario (“AG Ontario”), opposed it.
The test for intervention under the Ontario law is well established from Peel (Regional Municipality) v. Great Atlantic and Pacific Co. of Canada Ltd. (1990), 74 O.R. (2d) 164:
… in determining whether an application for intervention should be granted…the matters to be considered are the nature of the case, the issues which arise and the likelihood of the applicant being able to make a useful contribution to the resolution of the appeal without causing injustice to the immediate parties.
In P.S., Laskin J.A. noted the following specific considerations in a Charter case:
 In a Charter case, the proposed intervener usually has to establish at least one of three criteria: it has a real, substantial and identifiable interest in the subject matter of the proceedings; it has an important perspective distinct from the immediate parties; or it is a well-recognized group with a special expertise and a broadly identifiable membership base: Bedford v. Canada (Attorney General), 2009 ONCA 669, 98 O.R. (3d) 792, at para. 2.
The respondents conceded that the proposed interveners met at least one of the Bedford criteria but they submitted that the proposed interventions were inappropriate under the latter prongs of the Peel test – they argued that the CCLA would not make a useful contribution because its arguments were either duplicative of the appellant’s or directed to uncontested issues, and the MHLC would cause injustice because it proposed to raise a new issue not raised before the application judge.
Laskin J.A. rejected these arguments. With respect to the CCLA, he held:
 I am satisfied that the CCLA will make a useful contribution to the court’s understanding of the issues and therefore should be granted leave to intervene as a friend of the court. As a national organization concerned with the protection of civil liberties generally, the CCLA can offer its views on the systemic implications of the outcome of the case. This is a perspective that is not otherwise reflected in the appellant’s submissions. …
 I am also satisfied that there are live issues between the parties about the extent to which the Charter applies to Waypoint and about the measures it must take to accommodate Mr. S.
 Although I agree that the potential exists for some overlap between the CCLA’s arguments and those of Mr. S., Mr. Morritt [counsel for the CCLA] has undertaken to ensure that his submissions will not be repetitive. That undertaking should be sufficient to alleviate Ontario’s concerns about the CCLA’s intervention.
Regarding the MHLC, AG Ontario, in particular, argued that its proposed submissions on s. 24(1) of the Charter, and the rule of law and Canada’s international commitments, were new issues. Laskin J.A. easily determined that the submissions concerning the rule of law and Canada’s international commitments were “not new, stand-alone issues but rather are interpretive tools to inform the court’s analysis of the principles of fundamental justice” (para. 18).
He then addressed the s. 24(1) issue, and in so doing, illustrated how to determine what is – and is not – a new issue on appeal, and how the issue of “prejudice” should be considered when determining whether to decline to grant a motion for intervener status:
 Whether the MHLC should be permitted to argue that the Consent and Capacity Board has s. 24(1) jurisdiction is a more difficult question. On my reading of the materials, Mr. S. did not take the position that the Board has, or should be deemed to have, the power to grant remedies under s. 24(1). On the contrary, the crux of Mr. S.’s argument both before the application judge and on appeal is that the MHA [Mental Health Act] scheme is unconstitutional precisely because the Board’s jurisdiction is limited to affirming or rescinding a person’s involuntary status (and since 2010, ordering a transfer to a different facility); it has no power to supervise the terms of the person’s detention with a view to maximizing the person’s liberty. It appears to be implicit in his argument that the Board also lacks the power to grant s. 24(1) remedies for individual breaches of the Charter.
 Viewed in this way, I am not persuaded that the MHLC’s submissions on the Board’s potential s. 24(1) jurisdiction raise a new issue. Rather, those submissions arise logically out of the issues already squarely before the court on the appeal. Mr. S.’s primary submission is – and has consistently been – that the involuntary detention and review scheme created by the MHA is wholly inadequate to address the needs of long-term involuntary detainees like himself. To analyse that submission, the court will have to consider the scheme as a whole. That may include a consideration of any remedial powers the Board does or does not have to redress Charter breaches.
 This is not a case like Bedford v. Canada (A.G.), 2011 ONCA 209, 231 C.R.R. (2d) 113, in which the proposed interveners sought to argue not just that Canada’s prostitution laws violate ss. 2(b) and 7 of the Charter, as the applicants had successfully argued below, but also that the laws violate s. 15. …
 I am also not persuaded that the respondents would suffer any injustice if the MHLC is permitted to intervene. The MHLC submits that, in the light of Conway, the question whether the Board has s. 24(1) jurisdiction is strictly a matter of legal argument and will not require the parties to call any new evidence. I am inclined to agree.
 The Attorney General submits it might have chosen to lead evidence on the legislative history of the Board to establish that the legislature intended it to hold hearings concerning specific narrow legal issues in a very short time frame. In my view, these arguments go to the Board’s “statutory mandate, structure and function”, all of which can presumably be gleaned from an examination of the statute itself and relevant case law. At this stage, I do not anticipate a need for the parties to add to the record to address the Conway inquiry. However, if Ontario believes it is necessary to file fresh evidence, I will remain seized of the file and will case manage this or other issues that arise.
Both the CCLA and the MHLC were accordingly granted intervener status.