Real wages have declined in the U.S. since the 2009 recession and the lowest-paid workers are experiencing the steepest declines, according to a study by the National Employment Law Project.

In the period between 2009 and 2014, the 20 per cent of people in the lowest-paid occupations saw wage declines that averaged 5.7 per cent, researcher Irene Tung found.

For all workers, the purchasing power of their average wages declined by four per cent in the same period, meaning the cost of living outpaced any increase in pay.

Among the best-paid 20 per cent of the U.S. population, the drop in purchasing power was about 2.6 per cent.

But NELP found the steepest drop in purchasing power was among workers who were already poorly paid. Jobs in retail, food preparation, personal care aides, janitors, cleaners and home health aide were among those most affected.

For restaurant cooks, the decline amounted to 8.9 per cent; for food preparation workers, 7.7 per cent; and for home health aides, 6.2 per cent.

In the recovery since 2009, these are the sectors where much of the hiring has taken place, the report said.

"These findings suggest that the wage foundations for millions of new jobs over the coming years could be especially shaky and inadequate, providing little economic security," Tung wrote in her report.

"Workers in these jobs are typically less resilient to unemployment, illness, and other destabilizing life events, and as their numbers grow, so too will the con sequences of this instability," she added.

Tung recommends policymakers find ways to address the problem of falling real wages.

The U.S. central bank has several times pointed to the stagnation of wages as an indication the U.S. economy has not fully recovered.

If real wages fall, it hurts the economy as consumers cannot stimulate growth through spending if their wages are too low to make ends meet.