Service business with receipts over $100,000 and no seller's permit MUST register for a use tax permit
In California, service businesses do not have to obtain a seller's permit unless they are selling products. However, every state also collects a use tax, which is basically the same thing as a sales tax, but on products that are purchased out-of-state (i.e. on the Internet from out-of-state companies). With the growth of Internet purchases, California now requires any service business with receipts over $100,000 per year, to register for a use tax permit and report and pay taxes on these purchases.
Click here for more information on the required permit
Click here for the form.