Unions, wages, inflation, and deflation

According to the Bureau of Labor Statistics:

The Consumer Price Index for Urban Wage Earners and Clerical Workers
 (CPI-W) decreased 1.7 percent over the last 12 months 

So, here is a question: if a big reason for unions to negotiate a wage increase is to keep up with the uptick in the Consumer Price Index, will unions now negotiate for a wage decrease?
Just asking :-)