If you have received a T2200 (Declarations of Conditions of Employment) from your employer, then you are able to claim employment expenses. If you received at least part of your income from commissions, then on your T4 you will have an amount in box 42 (only if you have commissions from employment would you see box 42, it would be in one of the 6 boxes at the bottom of the T4). If you do not have income from commissions, then you can not claim expenses as a commissioned employee. If you are a commissioned employee, you have the option of claiming as a commissioned employee or as a salaried employee. As a commissioned employee, there are more types of expenses that you are able to claim, however the expenses are limited to the amount of the commission (the amount in box 42 of the T4). If you are a salaried employee, there are fewer types of expenses that you are able to claim, however the limit is the total income shown in box 14. So, if you have no income from commissions, you have no choice, but have to claim from a smaller range of expenses...if you are commissioned, you can choose which way benefits you more. Claiming a wider range of expenses may not benefit the employee so much if the actual commissions are low.
Remember that you can only claim if you have the appropriate documentation from your employer, however below I have links to expenses that can be claimed by Salaried Employees and Commissioned Employees.
List of expenses that can be claimed as a salaried employee: http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns206-236/229/slry/menu-eng.html
List of expenses that can be claimed as a commissioned employee: http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns206-236/229/cmmssn/menu-eng.ht...
