"Businesses demand workers and the workers are supposed to magically appear," economist Joel Naroff said in a note this week to clients of Naroff Economic Advisors. ""But wages need to rise to attract the needed workers."
So far, that hasn't happened. While job openings overall are up nearly 20 percent in just the past year, wages have only risen by about 2 percent—roughly the rate of inflation. In real terms, wages have been flat. That may help explain why employers complain they can't fill some jobs.
But many hiring managers blame a shortage of skilled workers. When Express Employment Professionals, a staffing firm, recently surveyed its local franchises, some 83 percent said it was "somewhat difficult" or "very difficult" to fill job openings, up from 78 percent last year. More than half said they couldn't find enough qualified candidates.
Some jobs are harder to fill than others. Companies surveyed by Manpower Group, another staffing company, said the toughest occupations are skilled trades, sales reps, truck drivers, IT workers, accountants, engineers, managers and teachers.
Read MoreWhat companies are, and aren't, doing to find qualified workers
Despite these perceived shortages, employers have made little effort to lure qualified workers with higher wages. The leisure and hospitality industry, for example, had roughly 4.5 job openings for every 100 industry workers in May, according to the latest data from the Bureau of Labor Statistics. But wages are up just two-tenths of a percent in the last year; in real terms, they've fallen.
The same holds for workers in most industries, where wages haven't kept up with inflation—despite the pickup in demand from employers.
Read More Why state tax cuts aren't driving job growth
"Except for those at the top, wages have consistently declined over the past few years," said Rebecca Smith, deputy director of the National Employment Law Project, an advocacy group for workers.
Workers aren't the only one eyeing wage gains warily. The Federal Reserve is keeping a close watch on the pace of job openings and hiring as a possible signal that inflation may begin to pick up.