If, last month, the motion was moved, seconded, and stated by the chair, then it was in the assembly's hands last month. If that is the case, I assume it was (a) being discussed at last month's meeting when the meeting adjourned, or (b) was postponed to this month's meeting.
If, on the other hand, the motion was "moved" last month with the intention from the start that it would only be debated at this month's meeting, then the mover effectively just gave "notice of motion" last month's meeting. In that case, if the person who gave notice is not present this month, any other member can move the motion.
It sounds, from your wording, that your union has a particular custom or Special Rule of Order regarding the introduction of motions.