Tan – Tax Court of Canada states that not obtaining a GST number before claiming an input tax credit will result in denial of the ITC

Masse DJ stated, following Systematix and Comtronic, that if a registrant has not obtained an invoice specifying the prescribed information, including the GST/HST registration number of the supplier, before an input tax credit is claimed, the ITC will be denied. Although where, as here, the registrant still had not gotten the registration number by the trial date, denial of the ITC was to be expected, this would represent a harsh approach in more sympathetic circumstances, e.g., where absence of a registration number on the invoice was identified after claiming the ITC – with documentation of the missing particular then obtained before a CRA audit.

Neal Armstrong. Summary of Tan v. The Queen, 2015 TCC 121 under ETA – s. 169(4).