Why does local delivery on Shopify require an HS Tariff code?

Today, Shopify Shipping is not allowing me to ship locally. It won’t allow me to ship within my city without a HS Tariff code. I’ve moved all my shipping to ClickShip. What kind of Quality Control testing do they do?

It’s tedious but you can ship locally if you input the HS codes. I’ve had to do that on every one of my orders this afternoon.