Can the Tax Office collect while my objection is still pending?
By default yes — objection does NOT suspend payment. But you can request DEFERRAL — which the Collector must grant on "reasonable" objection.
Important misconception: an objection does NOT automatically suspend payment. A separate action is required: a request for payment deferral at the Collector (a separate Tax Office branch). Under Collection Act art. 25 + Collection Guidelines the Collector must grant deferral if your objection is "reasonable" — a low bar, plausible not proven. During deferral: NO collection, NO BKR registration, NO collection interest (but a running 3% per year accrual). Request: "Uitstel van betaling" form at belastingdienst.nl or letter with assessment number + reference to pending objection. On refusal: object within 6 weeks at the same Collector; on continued refusal: appeal to court.