The U.S. manufacturing sector contracted unexpectedly in November, dropping to its lowest level in more than three years in a sign the sector may be struggling to maintain momentum, according to an industry report Monday. The Institute for Supply Management (ISM) said its index of manufacturing activity fell to 49.5 last month from 51.7 in October. Te reading was below analyst expectations of 51.3. In the ISM index, a reading below 50 indicates contraction in the manufacturing sector, while a figure above 50 reflects expansion. In November, the index hit its lowest point since July 2009 and contracted after two consecutive months of growth that followed a weak period over the summer months. The report’s manufacturing employment index fell to 48.4 and was below 50 for the first time since mid-2009. New Orders fell to 50.3 last month from 54.2 in October and were at their lowest since August. The U.S. manufacturing sector was the key engine of growth following the 2007-2009 Great Recession, but the sector has slowed this year as other parts of the economy gradually have improved.