Do I need to resgiter for GST/HST?

I am working full-time (salary 70k), but I will also be soon giving consulting services to a non-profit on the side. I already registered for a business number with CRA.

However, the total charge I'll be billing this non-profit is 12k for the entire contract. Would I have to register by GST/HST? If not, does this mean I can't charge them tax at all on my invoices? Thank you!