WASHINGTON (BLOOMBERG) - Companies adding fewer workers to US payrolls in June than than the prior month indicates the job market may be moderating, data from the ADP Research Institute showed Thursday.

Private payrolls rose by 158,000 last month, according to ADP, compared with the median estimate of economists for a gain of 188,000. May's gain was revised to 230,000 from 253,000.

The second-lowest increase in 2017 probably reflects the challenge of finding skilled workers amid a tightening job market, and may also be a sign businesses are holding off on expansion plans until they see more evidence the new administration's plans are translating into legislation that will reduce taxes and spur growth.

The ADP report may prompt some economists to adjust their forecasts for the private payrolls tally in the June jobs report due from the Labor Department on Friday, where the median estimate is for a gain of 170,000.

"The job market continues to power forward," Mark Zandi, chief economist at Moody's Analytics, said in a statement. Moody's produces the figures with ADP.

"At this pace, which is double the rate of labor force growth, the tight labor market will continue getting tighter."

Hiring in construction fell by 2,000 after a 23,000 increase; factories added 6,000 workers Professional and business services led with a 69,000 gain; education and health services added 28,000 people; trade, transportation and utilities rose by 30,000.

Companies employing 500 or more workers increased staffing by 50,000 jobs; payrolls jumped by 91,000 at medium-sized businesses, or those with 50 to 499 employees; while small companies' payrolls rose by 17,000.