Final answer:
Primary authority in tax law includes the Internal Revenue Code, tax treaties, Treasury regulations, IRS rulings, and federal court case law, all of which serve as official legal sources with legal force in taxation.
Step-by-step explanation:
Primary authority in tax law refers to the official legal documents that carry the weight of law in tax-related matters. This includes the Internal Revenue Code (IRC), tax treaties, regulations promulgated by the Secretary of the Treasury, Internal Revenue Service (IRS) rulings, and case law established by the federal courts.
Specifically, the supremacy clause and necessary and proper clause grant Congress the authority to impose and collect taxes. Additionally, revenue generated by these taxes, such as federal income tax, is the major source of federal government income.
Federal tax revenues finance various governmental expenditures, ensuring the functioning of the government and the provision of public services.