Researching treaties to which the United States may not be a party can be a challenge. Multilateral treaties are usually the easiest, as they are published in sets like the United Nations Treaty Series (UNTS), and on various web sites. Of course, only those treaties deposited with the UN Secretary General will become part of the UNTS. Although most multilateral (and many bilateral) treaties are deposited with the UN, states are under no obligation. For more information on the role of the UN as a treaty depository, see the Summary of Practice of the Secretary-General as Depository of Multilateral Treaties on the UN website, or consult the Treaty Handbook , 4th Floor, KZ1302 .T73 2013 - both were written by the Treaty Section of the . Office of Legal Affairs. To contact the . Office of Legal Affairs, Treaty Section, call (212) 963-2523 or email them at treaty@ .
Many countries provide publicly funded retirement or health care systems.  In connection with these systems, the country typically requires employers and/or employees to make compulsory payments.  These payments are often computed by reference to wages or earnings from self-employment. Tax rates are generally fixed, but a different rate may be imposed on employers than on employees.  Some systems provide an upper limit on earnings subject to the tax. A few systems provide that the tax is payable only on wages above a particular amount. Such upper or lower limits may apply for retirement but not health care components of the tax. Some have argued that such taxes on wages are a form of "forced savings" and not really a tax, while others point to redistribution through such systems between generations (from newer cohorts to older cohorts) and across income levels (from higher income levels to lower income levels) which suggest that such programs are really tax and spending programs.  Some tax scholars argue that supporting social security programs exclusively through taxes on wages, rather than through broader taxes that include capital, creates distortions and underinvestment in human capital, since the returns to such investments will be taxes as wages.