From NALC:

Fourth Contract COLA: -0-

There will be no fourth cost-of-living adjustment (COLA) for letter carriers this period, under the terms of the 2006-2011 National Agreement. That’s because there was no increase in the Consumer Price Index (CPI) between July 2008 and January 2009, based on figures released by the Bureau of Labor Statistics (BLS) February 20,

The next COLA—the fifth under the contract—will be based on any increase in CPI from January to July 2009. The last COLA was $1,497 in September 2008.

There are eight COLAs included in the 2006-2011 agreement.

From APWU:

In January, the Consumer Price Index (CPI-W) rose to 612.719, still well below the July 2008 index of 644.303 (upon which our last COLA was based). After the final month of the six-month measuring period, the fifth COLA under the 2006 National Agreement and the Operating Services Agreement will be zero.