When you make a payment for membership, at the bottom of the page there is a line asking whether or not you want to donate $1 to this group. The box is already checked and you have to un-check it in order not to donate. You just didn't see it. TER or iBill (don't know who's behind the donation) has no way of knowing if you wanted to or missed it, they just see a checked box. So you actually did authorize it.