Job seekers stand in line to meet with prospective employers at a career fair in New York City. REUTERS/Mike Segar The US economy's biggest problem will soon be a lack of available workers, according to ADP Research Institute.

"Businesses are having a more difficult time filling open job positions, which are near record highs," Mark Zandi, chief economist of Moody's Analytics, said in a report.

The institute's monthly report on private payrolls, out Wednesday, showed an increase of 179,000 in July.

Economists had forecast a rise of 170,000, according to Bloomberg. The gain in June was revised up by 4,000, to 176,000.

But the overall pace of job creation is slowing as the economy approaches full employment, which is a level where virtually all who are willing and able to work are employed.

Some economists see a slowdown in the number of people businesses are hiring as the natural outcome of an unemployment rate as low as 4.8%, although weaker capital spending and lackluster earnings growth have raised separate concerns.

"As the labor market continues to tighten, small businesses may increasingly face challenges when it comes to offering wages that can compete with larger businesses," Ahu Yildirmaz, head of the ADP Research Institute, said in the release.

Goods-producing companies lost 4,000 jobs, fewer than in June, as manufacturing employment increased. The construction industry lost 5,000 private payrolls.

This data comes ahead of the Bureau of Labor Statistics' numbers on Friday, which are projected to show an increase of 180,000 in nonfarm payrolls.