A BLS news release said the slight decline stems from the 0.3% decrease in average weekly hours and a 0.1% increase in the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W), which were partially offset by a 0.2% increase in average hourly earnings.
Average weekly earnings climbed 4% from January 2006 to January 2007. After deflation by the CPI-W, average weekly earnings increased by 2.1% according to the news release.
Average weekly earnings were $573.48 in January 2007, compared to $558.71 a year earlier, before adjustment for seasonal change and inflation.
A breakdown by industry can be found here .