June's index reading of 56.2 represents further slowing from the index's 12-month high of 60.4 in April.

Any reading above 50 indicates expansion; however, economists expected a reading of 59 for June, The Associated Press reported.

"We are now 11 months into the manufacturing recovery, and given the robust nature of recent growth, it is not surprising that we would see a slower rate of growth at this time," said Norbert Ore, chair of the institute's manufacturing business survey committee. "The sector appears to be solidly entrenched in the recovery."

Growth in the second half of 2010 isn't expected to be weaker than in the first half, Ore said.

The employment portion of the index fell to 57.8 in June from 59.8 in May.