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Answer for If you discover an issue, how far back to you need to amend T4’s for your employees (in Ontario?) I cannot find a straight answer.

Here you go. This comes from our payroll expert, Alan McEwan.
There are really two answers:

  1. The employer’s obligation is to report the correct amounts on each T4 slip. If one of the boxes has been reported with an incorrect value, its as if the slip itself was never filed. There is no expiry date on the requirement to file a slip, so if an error is discovered an amended slip is required, no matter how old the error is.
  2. So long as there is no fraud involved, i.e. the deliberate misrepresentation of income, then the dates that limit the CRA’s ability to re-assess income apply or 6 years. In other words, for the 2014 T4s, no amendment would have to be file after December 31, 2020.