U.S. manufacturing activity sank a little deeper into contraction in May, reflecting persistent worries over the impact of the Trump administration's whipsawing trade policy, according to the Institute for Supply Management (ISM).

The ISM purchasing managers' index of manufacturing activity fell to 48.5 in May, from 48.7 in April, matching a consensus of economists polled by The Wall Street Journal.

"That brought the index to its lowest level since November, as activity fell further below the 50-mark that divides growth and contraction," noted the newspaper in its report on Monday. "It was last above 50 in January and February, though that followed 26 consecutive months of contraction."

Measures of demand were mixed, said Susan Spence, chair of the ISM Manufacturing Business Survey Committee. New orders and backlog of orders indexes declined at slower rates than April, though customers' inventories and new export orders contracted more strongly.

Excluding the pandemic period, new export orders were at their lowest reading since 2009. The survey's measure of imports sank sharply for a second straight month. Price growth remained high, though moderated compared with April, while the survey's production index increased from an alarmingly low reading in the prior month, Spence said.