Runsten said that one possible explanation for this rapid increase is that low-wage workers aren't moving up the income ladder and can't escape "dead-end, low-wage jobs."

But others say this merely reflects the fact that many low-income workers who arrived here 10 to 15 years ago have tended not to move around, focusing instead on making sure their children get better jobs.

The LAANE study also found that the largest number of working poor 245,000 is in the manufacturing sector, with 90,000 of those working in the garment industry. Retail was a close second with 218,000 working poor, half of those people working in restaurants and bars. Personal services including hotel workers and domestics came in third, with 98,000 in the ranks of the working poor.

Despite its reputation for high-wage jobs, the construction sector has roughly 80,000 working poor, according to the LAANE study.

"It really shows the dual nature of construction," said Jack Kyser, chief economist for the L.A. County Economic Development Corp. "Union construction workers are very well paid, but then there are the people on street corners getting day-laborer jobs."

Many of these people are recent immigrants, a fact borne out by the disproportionately high number of Latinos among the working poor at 73 percent, almost twice the 40 percent Latino representation in the overall workforce.

For reprint and licensing requests for this article, CLICK HERE.

Next