Private companies in the U.S. added 128,000 jobs in May, indicating slower job growth in a tight labor market, payroll data company Automatic Data Processing (ADP) reported Thursday.

"The job growth rate of hiring has tempered across all industries, while small businesses remain a source of concern as they struggle to keep up with larger firms that have been booming as of late," said Nela Richardson, chief economist at ADP.

Large firms hired 122,000 workers, medium-sized businesses added 97,000, while small companies cut 91,000 employees, the report showed, indicating an unbalanced recovery across different company sizes.

In February and April, small companies also slashed jobs as large firms and medium-sized businesses saw payroll gains, according to the report, produced by the ADP Research Institute in collaboration with Moody's Analytics.

Small companies – those with fewer than 50 employees – have lost nearly 300,000 jobs since February as they struggle to hire and retain workers looking for better pay and benefits in a tight market.

The service sector saw a job gain of 104,000 in May, while the goods-producing sector added 24,000 jobs, the report showed.

"Under a backdrop of a tight labor market and elevated inflation, monthly job gains are closer to pre-pandemic levels," said Richardson.

The ADP report came one day before the crucial monthly employment report to be released by the Labor Department's Bureau of Labor Statistics with employment data from both the private sector and the government.