Code of Federal Regulations Title 39. Postal Service § 39.3030.141 CPI–U data source

The monthly CPI–U values needed for the calculation of rate adjustment limitations under this subpart shall be obtained from the Bureau of Labor Statistics (BLS) Consumer Price Index—All Urban Consumers, U.S. All Items, Not Seasonally Adjusted, Base Period 1982–84 = 100. The current Series ID for the index is “CUUR0000SA0.”