U.S. manufacturing barely expanded last month as factories cut back sharply on production, and new orders plunged.

The Institute for Supply Management, a trade group of purchasing managers, said Monday that its index of manufacturing activity fell to 51.3 in January from 56.5 in the previous month.

That's the lowest reading since May and suggests that factories are slowing slightly at the start of the year. Still, any reading above 50 signals growth.