The Institute for Supply Management (ISM) figure for June came in at 46 percent, down from 46.9 percent last month, the ISM said in a statement.
This was well below the median forecast of economists surveyed by MarketWatch.
A reading below 50 percent indicates that the manufacturing sector is generally contracting.
Of the six largest manufacturing industries, only transportation equipment saw growth last month, according to the ISM survey, underscoring the difficulties facing the manufacturing sector at-large.
The ISM data indicates the contraction in the sector is picking up pace, at the same time as other sectors of the U.S. economy show signs of unexpected buoyancy.
"The June composite index reading reflects companies continuing to manage outputs down as softness continues and optimism about the second half of 2023 weakens," ISM Business Survey Committee Chair Timothy Fiore said in a statement.
"Demand remains weak, production is slowing due to lack of work, and suppliers have capacity," Fiore said.
"There are signs of more employment reduction actions in the near term," he added.