Unsurprisingly this topic has not gone away despite TTC management stating that it would not prefer interest arbitration. To be honest the only reason I can see for pushing this idea is populism. Three city councilors are encouraging people to sign a petition but the petition has several problems. Their petition lacks specifics such as what sort of interest arbitration system would be imposed, who the arbitrator would be or at least the criteria for selection, ... and so on. Obviously I disagree with their approach, for now I will outline two reasons I question making the TTC essential.
1) The definition of essential services in section 30 of the Crown Employees Collective Bargaining Act states;
30. In this Part,
"essential services" means services that are necessary to enable the employer to prevent,
(a) danger to life, health or safety,
(b) the destruction or serious deterioration of machinery, equipment or premises,
(c) serious environmental damage, or
(d) disruption of the administration of the courts or of legislative drafting;
It is difficult to see how the TTC fits into any of these categories. No doubt a TTC strike is inconvenient for the entire city, but inconvenience, does not make something an essential service.
2) The outcomes that a interest arbitration process might create. Below I have cited a few articles I came across after a Google Scholar search.
Regulating Labor Conflict In Public Sector Labour Relations: The Ontario Experience, found that bargaining units covered by compulsory interest arbitration arrive at impasse in bargaining 8.7 to 21.7% more often than in right to strike sectors. This implies that by taking away the threat of strikes and conversely lockouts the parties will be more likely to dig in their heals and resort to the interest arbitration process.
Interest Arbitration, Outcomes and the Incentive to Bargain by Henry S. Farber and Harry C. Katz at MIT
(From the articles preface) This study develops a model of bargaining that demonstrates that an interest arbitration procedure will encourage negotiated settlements to the extent that risk aversion dominates the preferences of the parties and there is uncertainty regarding the arbitrator's behavior. The authors conclude that it is likely that risk aversion does dominate preferences, but the evidence is not conclusive. They also argue that uncertainty may be reduced over time for various reasons, leading to increased use of arbitration and a convergence between the terms of negotiated and arbitrated agreements.
Anyone interested in the topic (beyond mere populist rhetoric that is) should really try to read some of the literature out there on this topic - there are a wealth of well researched and thought out papers.