Bank policy states that employees must bring any OD balance current within the next pay period.
We are looking at disciplinary action against the employee for violation of the policy on NSF. Would there be any issues with this?
No issue with disciplinary action in response to a policy violation. But I would suggest that you confirm that a policy violation did indeed happen. The wording that you shared here makes me wonder if the OD should be rectified before the employee's next pay, or with the employee's next pay, or in the pay period that follows the employee's next pay.
Whatever it says, make sure it is clear to the people who need to read it, understand it, and abide by it before enforcing it.