Baggersup asks:
Though if the reports that BA sends BASSA an update every month is true, I wonder why that's possible? Hm.
It has been common for many years for businesses to deduct union dues from payroll and transmit the deductions to the union. Employess who wish to manage union subscriptions in this way have obviously given the company permission to make the deductions and to have the union informed that they wish to subscribe in this way. so the company has a lower bound on the number of employees who are union members; the number may be swelled by other individuals who choose, for whatever reason, other payment methods.