Information on this subject provided on the Canada Revenue Agency website:
How to report employment income during COVID-19 pay periods
For the tax year 2020, in addition to reporting employment income in Box 14 or Code 71, use new other information codes when reporting employment income and retroactive payments in the following periods:
Code 57: Employment Income (March 15 to May 9)
Code 58: Employment Income (May 10 to July 4)
Code 59: Employment Income (July 5 to August 29)
Code 60: Employment Income (August 30 to September 26)
Eligibility criteria for the CERB, CEWS, and CESB is based on employment income for a defined period. The new requirement means employers should report income and any retroactive payments made during these periods.
If you are reporting employment income for the period of April 25 to May 8, payable on May 14, use code 58.