The employment services industry, which includes both
temporary staffing agencies and more permanent employee
leasing firms, is expected to rank among the fastest-growing
sectors in the country in the next decade.
Staffing work is one part of a larger story about the declining middle
class in our country. More and more, major corporations are separating
themselves from the workers who make their products and supply
their shelves by inserting labor intermediaries who are nominally the
“employers” of these workers.
The competition between staffing agencies to undercut rivals’ bids
places downward pressure on wages and working conditions. Staffing
agencies may take over all of the former employer’s responsibilities
for wages, health and safety, compliance with discrimination laws, and
provision of workplace benefits. But they still need to make a profit. This
means that working conditions almost necessarily must degrade when a
host company turns to a staffing agency. Intense competition produces
intense pressure to cut costs by whatever means necessary, leading some
to seek out the most vulnerable workers,  cut corners, and cheat.

http://www.nelp.org/page/-/Reports/Temped-Out.pdf?nocdn=1