CRA considers discounts on purchases by members of a public sector body to be “insignificant” for GST exemption purposes if less than 30% of membership fees

Membership fees in a public sector body can be GST-exempt even where the member receives discounts on purchases made from the body provided that their total value is “insignificant” relative to the membership fee, which CRA interprets as being less than 30%.

Neal Armstrong. Summary of 2 June 2015 Ruling 169081 under ETA Sched. V, Pt. VI, s. 17(e).