This is from a new paper by Tania Voon:
... Discrimination and trade-restrictiveness are two distinct concepts that, while overlapping, should not be conflated. A non-discriminatory internal measure is unlikely to restrict trade, because it is unlikely to reduce the competitive opportunities of imported products vis à vis
domestic products. A discriminatory internal measure may act as a barrier to trade and therefore be trade-restrictive. However, discrimination is not necessary to establish trade-restrictiveness, because trade-restrictiveness can exist without discrimination, for example in the case of an import ban that operates in conjunction with corresponding restrictions on domestic production or sales.
I haven't read the whole paper (just gave it a quick skim), so maybe Tania addresses this, but my question has always been whether there is a qualitative difference between discriminatory measures, on the one hand, and non-discriminatory measures that restrict trade, on the other. Thus, when measuring the degree of trade-restrictiveness, you might want to consider discriminatory measures as more of a problem because of the way in which they restrict trade. A product ban might prohibit trade completely, and thus quantitatively it is worse, but there is something particularly nefarious about discriminatory measures.