In Association des pompiers professionnels de Québec inc. c. Québec (Ville de), 2013 QCCA 208, the issue was the scope of solicitor-client privilege. The city of Québec had secured a legal opinion regarding the restructuring of its fire service. Restructuring was opposed by the union, which made multiple complaints to the labour relations board (the Commission des relations du travail). One of these was for interference in union activities.
It was in the context of this complaint that the CRT ultimately ordered the city to hand the opinion over in its entirety to counsel for the firemen. The reasoning of the CRT appeared to be that the director-general of the city had waived privilege by relying in her testimony on the conclusions of the legal opinion to demonstrate that she had acted in good faith.
The Court acknowledged that the categories of decision to which the intrusive correctness standard of review applies are narrowing. Nonetheless, it took the view that solicitor-client privilege requires uniform application regardless of the particular administrative context:
 Il en va autrement en matière de secret professionnel de l’avocat. Peu importe le contexte, en pareille matière, les conditions d’application et de renonciation à un tel droit fondamental demeurent les mêmes. Les organismes administratifs aux prises avec une question de renonciation au secret professionnel doivent statuer correctement sur ce point. L'importance de la question du respect du secret professionnel pour le système juridique est fondamentale et doit être tranchée de manière uniforme et cohérente, étant donné ses répercussions sur l'administration de la justice dans son ensemble...It is also worth noting that professional privilege has quasi-constitutional status in Quebec, where it is protected by s. 9 of the Quebec Charter.
I am willing to be persuaded otherwise, but this result seems right to me. Professional privilege is something that requires uniform application across regulatory regimes. A lawyer, for example, ought to be able to give frank legal advice regardless of the particularities of the context. It would be odd if a lawyer felt obliged to advise a client differently on the same issue depending on whether it arose before a court or an administrative tribunal which had developed a unique line of reasoning with regard to privilege.
This is quite unlike the application of, say, the rules of evidence, which an administrative decision-maker can tailor to fit a particular context. It would have quite the opposite effect, by requiring professional advisers to tailor their advice to a particular context. This may undermine the lawyer's duty of candour and lead to similarly situated clients being treated unequally.
Quite apart from these pragmatic considerations, the quasi-constitutional status of professional privilege suggests that resolution of privilege questions has not been delegated to administrative decision-makers. Moreover, professional privilege is a question on which courts have a great deal of expertise.
On the merits, the CRT was wrong (and did not expressly address the waiver question (at para. 23). The director-general's references to the opinion in her testimony were extremely limited and did not amount to a clear waiver of privilege over the entirety of the opinion (at para. 24). A partial waiver was present and the city had indeed handed over the relevant portions of the retainer and opinion (at para. 29). There was no basis for the CRT to go any further.
H/T Karim Renno.
UPDATE: Given the influence of the Quebec Charter in this case, it would be remiss of me not to mention Lethbridge Regional Police Service v Lethbridge Police Association, 2013 ABCA 47, where the Alberta Court of Appeal held that the appropriate standard of review on "human rights issues" is correctness (at para. 28). To be fair, this follows a consistent line of Supreme Court of Canada cases beginning with Canada (Attorney General) v. Mossop,  1 SCR 554. I have always preferred the dissent in that case. We will have to wait and see what the Supreme Court of Canada says whenever a "human rights issue" pops up on its docket.