Shipping Delay

Hi everyone. I ordered my new iMac a couple weeks back and it shipped July 16th. The standard delivery date was Monday, July 26th but the scheduled delivery date was Thursday, July 22nd. however, I just checked the tracking information and got a notification that says "Clearance delay - Import Shipment requires a Commercial Invoice." Does anyone know what this means? Or has this happened to anyone else with their Apple products, if so how long did it take for it to clear?