When to Recruit Employees Already on the Payroll
Unfortunately, in some school systems, there are a few people who do not pay their dues. They have found a "reason" that makes them comfortable as non-joiners. They don't pay their share and tend to resent being asked to do so.
The best time to recruit these people is during the year (not during September when you are recruiting the new employees.) Remind them occasionally during the year that the association has negotiated their salaries and fringe benefits, that the law requires you to represent them, and their colleagues expect them to pay their share of the costs of representation.