How Do I Object to a GST/HST Assessment in Canada, and Who Handles It?

This answer covers Canadian federal tax law, which applies in every province.

You object to a GST/HST assessment within 90 days after the day the notice of assessment was sent, on the prescribed form, setting out the reasons and all relevant facts. CRA says to file with Form GST159 by mail or fax to the Chief of Appeals at the Appeals Intake Centre in Sudbury, or online through My Business Account using "Register my formal dispute".

Online objections go directly to the Appeals Division for validation and review, and representatives can use Represent a Client. The Minister may accept an objection not filed in the prescribed manner. Certain larger "specified persons" must also describe each issue, state the relief sought and give facts and reasons, with 60 days to fix missing information.

Collection differs from income tax: CRA says it can keep collecting amounts you owe while the objection is pending, and interest still applies, though you can pay all or part of the disputed amount to limit it. If you disagree with the result, you can appeal to the Tax Court once the Minister confirms or reassesses, or 180 days after filing with no decision, but not after 90 days from the notice of confirmation or reassessment. In Quebec, Revenu Québec generally administers GST/HST.