Collection of union subs
A. No. You will need to check whether the members have notified the employer in writing that they are exempt from paying the political levy (just sending on their exemption notice to the union is sufficient).
Once they have provided this to the employer, it must stop making the full deduction as soon as is reasonably practicable.
Under section 86 Trade Union and Labour Relations Consolidation Act 1992 (TULRCA), the employer cannot refuse to operate check-off on the basis that it has received an exemption certificate.
If the employer were foolish enough to follow through with its threats, the burden of proving why it acted would be on it. In particular, under section 87(3) TULRCA the employer would be obliged to show what possible other reason there was for its action.