If your employer is a GST Registrant and you are claiming Employment Expenses on the T777, you may be able to claim the GST Rebate. The CRA guide lists which expenses qualify for the rebate and states the following:
"As an employee, you may qualify for the GST/HST rebate if:
- you paid the GST/HST on certain employment-related expenses and deducted those expenses on your income tax return; and
- your employer is a GST/HST registrant"