The Institute for Supply Management, a trade group of purchasing executives, says its index tracking service-oriented companies dipped to 53.8 last month from 55.4 in May.
A reading above 50 indicates expansion. Economists polled by Thomson Reuters expected a reading of 55.0 for June.
A robust service sector, which accounts for about 80 percent of U.S. employment, is crucial to keeping the economy growing and adding jobs.
ISM also says employers' plans to hire declined in June after growing in May for the first time in 28 months.
