The STM and its maintenance union are facing off before a labour tribunal over who's to blame for the recent bus shortages.
The STM requested a hearing before the Administrative Labour Tribunal alleging the union is conducting a pressure tactic campaign that is having an impact on the number of road-worthy buses and service to commuters.
The STM is trying to prove that since last year, there's a pattern of labour and union issues linked to delayed buses and an increase in the number of buses parked in the garage for maintenance.
With the help of a number of charts and graphs, Luc Mercier, director of bus maintenance services, testified that the number of buses available to go on the road decreased following events such as strike votes, strikes and even a threat of a strike.
Mercier said just over 1400 buses are required to provide optimal service, out of a fleet of 1800.
Mercier said that in the past week alone, 150 buses were off the road, something he's never seen in his eight years on the job.
Mercier testified that the labour conflict is also creating a bad working climate and having a negative impact on productivity
The lawyer for the union is arguing that the wild winter weather could be to blame for the frequent breakdowns and service delays in past weeks.
The union has said that staff shortages and poor decisions by management have resulted in more buses needing maintenance and being parked in the garage.