We are considering contacting a subset of certificants via phone if they are in danger of suspension to inquire why or if they intend to let their certification lapse, and if they don’t intend their certification to lapse, to help direct them to ways to complete their CPE requirement according to the CPE policy. Would we need to worry about this being any sort of threat to impartiality?

No threat to impartiality. I view it as a very nice service to your certificants.

Just make sure that if they say ‘No’ you don’t continue with your reminders.

And make sure to include it in your impartiality threat analysis, with a clarification that you don’t ‘cherry pick’ candidates with certain scores or credentials for these notifications.