The latest ADP figures showed that job gains slowed to 278,000 last month, more than analysts expected though still down from the revised 291,000 figure in April.
"Job growth is strong while pay growth continues to slow," said ADP in its report.
"This is the second month we've seen a full percentage point decline in pay growth for job changers," the company's chief economist, Nela Richardson. said.
She added that "wage-driven inflation may be less of a concern for the economy despite robust hiring."
For workers who changed jobs, wage growth stood at 12.1 percent last month, down one percentage point from April.
Those who stayed on saw pay gains of 6.5 percent in May, down from April as well.
While private sector employment gains were boosted by areas like leisure and hospitality, other industries such as manufacturing and finance lost jobs, according to ADP.
The figures come a day ahead of the Labor Department's employment report, which will be closely watched given the bearing it is likely to have on central bankers' policy decisions ahead.