What percentage of U.S. employees are factory workers?

Hello.

As of January 2003, just under 12 percent of U.S. employees were
factory workers.

According to the Bureau of Labor Statistics there were 16,441,000
factory workers in the U.S. out of a total employed workforce of
137,536,000. As such, factory workers made up 11.9539 percent of U.S.
employees. However, it's worth noting that factory jobs represent 14.4
percent of all employment covered by unemployment insurance.

The Bureau of Labor Statistics uses the term "manufacturing workers"
synonymously with "factory workers."
 
"Manufacturing is by far the largest of the goods-producing industries
in terms of employment. While factories account for just a little more
than a third of goods-producing establishments, manufacturing
employees outnumber their colleagues in construction and mining by
nearly 3-to-1. Manufacturing represents 5.4 percent of all
establishments and 14.4 percent of all employment covered by
unemployment insurance."
Bureau of Labor Statistics
http://stats.bls.gov/iag/iag.manufacturing.htm

Manufacturing jobs: 16,441,000 (January 2003)
Bureau of Labor Statistics 
http://stats.bls.gov/iag2/iag.manufacturing_t.htm

Total employment: 137,536,000 (January 2003)
Bureau of Labor Statistics 
http://www.bls.gov/news.release/empsit.nr0.htm

search strategy: "bureau of labor statistics", manufacturing, factory
jobs

I hope this helps.

Perfect answer!