Five Federal Reserve indexes of regional manufacturing all slumped in December, the first time they have fallen in unison since May 2016 and the latest evidence that a pillar of the U.S. economy has started to wobble heading into next year, Bloomberg reported.

The Dallas Fed’s factory index unexpectedly contracted this month, falling to a two-year low of minus 5.1 from 17.6 in November, and the steepest decline since 2013. The district bank covers the oil-producing region of Texas, northern Louisiana and southern New Mexico. Oil prices are down about 40 percent from a nearly four-year high in October.

More than 20 percent of manufacturers said that their outlook worsened this month, according to the regional Fed report released Monday. “Expectations regarding future business conditions remained positive but retreated notably in December,” it said.

Read the full story here.