The United States tax system is a system divided into federal, state and local levels. The US tax law sources on which the tax system is based are divided into legislative, executive and judicial sources. The main sources from the legislative branch are the Internal Revenue Code and Congressional Committee Reports, some of the main sources from the executive branch are Income Tax Regulations and Revenue rulings, while the main source from the judicial branch are court decisions. In the United States, individual taxpayers are divided into US citizens, resident aliens and non-resident aliens and their residency is determined by the green card test or the substantial presence test. Tax payers as legal persons are divided into sole traders, C corporations, partnerships, S corporations, and international corporations and limited liability companies. At the federal level, the Internal Revenue Service (IRS) is a government agency within the Department of the Treasury responsible for collecting taxes and enforcing tax laws. The organizational structure of the IRS is divided into a Commissioner, a Deputy Commissioner for Services and Authorities, and a Deputy Commissioner for Operational Support. The IRS is also divided into four divisions according to the types of taxpayers and these are the divisions for large and international companies, small companies and self-employed, exempt bodies and government bodies, and salaries and wages. At the state and local level, names of the tax authorities that are responsible for such tasks vary depending on the state in which they are located, for example the Department of Taxation and Finance. Although most tax disputes with the IRS are resolved administratively, if disputes do arise, the tax courts, which are divided into the Court of General Jurisdiction, the Court of Appeals and the Tax Court, are responsible for decisions on tax issues. The US federal tax system is divided into four elements, which are: (1) income/profit tax on individuals, estates, trusts and corporations, (2) payroll tax intended to finance certain social security programs, (3) tax on inheritance, gifts and transfer of property that skips a generation, (4) excise duties on certain goods and services. Most of the funds at the federal level are collected from income tax. Taxes prescribed at the state level depend on state legislation, and the state is not obliged to prescribe, for example, state income tax. At the state level, the most profitable forms of taxation are income tax and consumption tax, while at the local level, the most profitable form of taxation is the property tax. At the state level, there are other forms of taxation such as marijuana tax or soda tax.