From Service Canada
5. Can I work while on EI?
Yes, you must accurately report all earnings before deductions from employment, in the week(s) in which they were earned, as well as any other monies you may receive. If you are receiving regular, parental, or compassionate care benefits you can earn 40% of your weekly benefit rate or $75 , whichever is higher, without changing the amount of benefits you will receive for that week. This is called your allowable earnings. Any monies earned above your allowable earnings will be deducted dollar for dollar from your benefits. However, if you work a number of hours that is considered to be a full work week, you are not considered to be unemployed and not entitled to benefits for that week. For more information, please refer to the Full Work Week question.
There are no allowable earnings while receiving sickness or maternity benefits. Any monies earned will be deducted dollar for dollar from your benefits.
Re: Working and EI info
Yeah basically you cannot work during the first 17 weeks (that includes the 2 week waiting period) at all - or they take it back dollar for dollar.
You can earn 40% of your EI each week after that.
I was not aware of not being allowed to work during the first 17 weeks so I'm totally screwed.