When creating Meetings, an option to make the meeting mandatory should be available. By selecting the mandatory option, the meeting would function similar to a game in that it will show on the officials calendar and effect official availability. Conversely, an non-mandatory meeting would continue to function as it does today.
As officials' individual calendars can be shared among different associations/leagues and update simultaneously, this would help officials manage their calendars and availability better. It would also assist in preventing assignors from in other associations/leagues from scheduling the official when they need to attend a meeting.