The Chicago Purchasing Managers' Business Barometer fell to 46.2 in May from 52.3 in April, the National Association of Purchasing Management-Chicago said Friday.
The data is compiled on a seasonally adjusted basis. An index reading below 50 signals a slowing economy, while a level above 50 suggests expansion.
Economists polled by Thomson Reuters predicted a 53.0 reading for the index.
"April's positive move had suggested that the first quarter slowdown was transitory and had been impacted by the cold snap and port strikes," according to a release. "May's weakness points to a more fundamental slowdown with the Barometer running only slightly above February's 5½-year low of 45.8."
