This will serve as authorization for. of. Listed below are the taxing authorities in Hillsborough County, along with applicable telephone numbers.A Letter of Authorization for GST is an important document to share power. (NAME OF ALL PROPERTY OWNERS- Attach list if more than one), being first duly sworn, depose(s) and say(s):. 1. If any person wishes to address the Board, a sign-up sheet has been provided at the entrance of the meeting room. A letter of authorisation for GST is an essential document regarding taxation and business operations. GST credits receivable from, and GST payable to the ATO, are recognised in the Statement of Financial Position. The Board must be explicit in the Board minutes and in a letter to each committee member the precise powers that are delegated to a committee.