The Institute for Supply Management (ISM) reports that its May index came in at 46.9 percent, 0.2 percentage point lower than the 47.1 percent recorded in April.
This was lower than the median forecast of economists surveyed by MarketWatch.
A reading below 50 percent indicates that US manufacturing is generally contracting. The lower figure for May vis-a-vis April indicates the contraction in manufacturing is getting deeper.
The new manufacturing data provides the U.S. Federal Reserve with additional evidence of an economic slowdown as it mulls how best to respond to above-target inflation.
Members of the Fed's rate-setting committee are divided over whether to hike interest rates for an 11th time on June 13-14 to bring inflation back down to the bank's long-run target of two percent.
Amid signs of an economic slowdown, some members have suggested the U.S. central bank should skip an increase this time to allow for more time to look at the impact of existing hikes on the economy.
"The May composite index reading reflects companies continuing to manage outputs to better match demand for the first half of 2023 and prepare for growth in the late summer/early fall period," ISM Business Survey Committee chair Timothy Fiore said in a statement.
"However, there is clearly more business uncertainty in May," he added.