Job creation in the private sector slowed in October following strong gains in the previous month, ADP said on Nov. 2.
Businesses added 147,000 new positions for the month, well below a consensus analyst forecast of 165,000 jobs.
However, September's total was revised upwards by 31% to 202,000, suggesting labor markets ended the summer in a stronger position than originally thought.
The report arrives two days before the release of the highly-anticipated monthly employment report from the Labor Department.
Economic concerns are front and center in the final days of the bitter race for the presidency.
The Federal Reserve also is due to announce a decision on interest rate policy later Wednesday. Policymakers have disagreed on the health of job markets, with some believing the US has not yet reached full employment.
However, Mark Zandi, chief economist at Moody's Analytics, which helped produce the ADP employment report, said the slowdown in hiring suggests employers were having difficulty finding candidates, indicating tightening labor market.
"Job growth remains strong although the pace of growth appears to be slowing. Behind the slowdown is businesses' difficulty filling open positions. However, there is some weakness in construction, education and mining," Zandi said.
Copyright Agence France-Presse, 2016