As per our TurboTax article: T777 Tax Form: Statement of Employment Expenses In general, you have to pay for those expenses as a condition of employment and not be reimbursed. If you work from home, you have to use the space only for your work. In all cases, your employer must provide you with a completed T2200 form which should indicate which expenses you were required to pay.
Therefore, if your employer indicates the added cost you paid was needed for your work, then you should be able to claim it. You may wish to clarify this with the Canada Revenue Agency (CRA) by calling them at 1-800-959-8281.
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