Two First Nations and an environmental group have filed separate applications for judicial review on Oct. 27.
Natural gas engine firm says market uncertainty in Europe, Russia and China have affected revenue.
Buses are expected to be delivered by the first quarter of 2014.
But, obstacles around price and range are stifling consumer sales.
Bi-fuel system offers a combined fuel range up to 1040 km.
ISB6.7G to use the spark-ignited, stoichiometric-cooled exhaust gas recirculation technology.
Encana Natural Gas Inc. has opened a compressed natural gas (CNG) station in Strathmore, Alta. to serve its own natural gas-powered vehicles and to encourage others to switch to the cleaner-burning fuel.
AFS engine controller technology has been used successfully in three natural gas hybrid demonstration buses manufactured by Ashok Leyland, the largest manufacturer of buses in India.