How are payroll source deductions different from an ordinary income tax debt?
1. The CRA can commence collection action as soon as source deduction are overdue. An objection does not stay collection action.
2. Some limitation periods (assuming no negligent misrepresentation):
|CPP 22(3)||4 yrs from date am’t should have been paid|
|EI 85(3)||3 yrs after end of the year in which payment should have been made|
|ITA 152||Normal reassessment period|
3. The CPP and EI Act provide for only 90 days to apply to extend the time to file an appeal to the Tax Court.
4. The CRA can assess an employer for failing to withhold CPP contributions and EI premiums, but the CRA can assess an employer for income tax source deductions only if the employer withholds income tax and fails to remit it. (MacLeod v R,  4 CTC 2223 (TCC) and Suspended Power Lift Service Inc. v R, 2007 TCC 519) The CRA can impose penalties, however, for failing to withhold income tax.
Gergely Hegedus and Keith Hennel, “Employer Source Deductions: No Ordinary Tax Debts” 9:4 Canadian Tax Focus (November 2019)