Every segment of residential and nonresidential construction sectors added jobs in May, according to analysis by the Associated General Contractors of America.

Construction firms added 17,000 jobs in May and 273,000 over 12 months, as the sector’s unemployment rate fell to 6.7 percent, the lowest May rate since 2006.

“Construction employers continue to expand headcount as they adjust to growing demand for their services in many parts of the country,” says Ken Simonson, the association’s chief economist. “Right now the two most likely obstacles to the industry’s continued expansion are growing labor shortages and political gridlock that could curtail public sector investments in infrastructure and construction.”

Construction employment totaled 6,387,000 in May compared to 6,370,000 in April and 6,114,000 in May 2014, Simonson notes, adding that construction employment is at its highest level since February 2009. Residential building and specialty trade contractors added 8,500 jobs (0.3 percent) since April and 149,300 jobs (6.5 percent) over 12 months. Nonresidential contractors hired a net of 8,600 workers for the month and 124,300 (3.3 percent) since May 2014.