The order power can be used in the case of, as you said, “risk of imminent harm to national security, national economic security or competition that constitutes a significant threat to the safety and security of persons, goods, ships or port facilities or the security of supply chains”. However, the order can be issued only to a Canada port authority or a person in charge of a port facility. Just coming back to what I stated earlier, that in itself wouldn't enable the minister to issue it to anyone other than the port authority or whoever is in charge of that port authority. If you were looking at it from the perspective of a labour group, it would not be applicable in those terms.
Evidence of meeting #96 for Transport, Infrastructure and Communities in the 44th Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was c-26.
A recording is available from Parliament.