It depends on the intent for which data will be used.
CPI measures inflation as experienced by consumers in their day-to-day living expenses whereas ECI indicates whether employment cost changes are rising or falling

If the 'change in labor rate' data is used for, to adjust compensation so that purchasing power is maintained, then the CPI would be a good source. However, if data will used to compare salaries so that it remain competitive within the labor market, then the ECI could be used.