Use a restricted [[Booking Activities|booking activity]] rather than a percentage discount.
1. Create an activity called something like "Members Only" and set your discounted prices on it.
2. Open the membership tier and restrict it to that activity.
Only members of that tier will see the activity on the booking page, and only they can book it. Everyone else carries on seeing your public rates and never knows the other option exists.
This is the cleanest way to run two-tier pricing, because the member rate is a real price rather than a percentage off. You can also restrict a tier to particular rooms the same way.
Restrictions apply to members who are logged in, so if you allow guest bookings, consider switching to private bookings in [[Booking Settings]].
See [[Membership Tiers]].