I've always thought that the striking truck drivers would think twice about giving the replacement drivers any stick for crossing the picket if they were from the forces.
That said, I suspect it is simply a SOP contingency plan for the government for what they perceive to be "vital services". It's the same when the firemen went on strike, they drafted the army in. At the end of the day, the army will always do as they are asked, civilians are a little more difficult to convince.