The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU03032224
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Unemployment Level: Construction and Extraction Occupations [LNU03032224], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU03032224/, July 6, 2015.