The US Department of Treasury and the US Congressional Joint Committee on Taxation have published a technical explanation of the protocol, signed on 21 September 2007, amending the income and capital tax treaty between the United States and Canada signed on 26 September 1980, as amended by the protocols signed on 14 June 1983, 28 March 1994, 17 March 1995 and 29 July 1997 respectively. The protocol is still awaiting ratification by the United States Senate