The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU03032222
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Unemployment Level: Natural Resources, Construction, and Maintenance Occupations [LNU03032222], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU03032222/, August 5, 2015.