The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU02032210
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Employment Level: Construction and Extraction Occupations [LNU02032210], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU02032210/, June 30, 2015.