A category of nontariff barriers to trade, TBTs are the widely divergent measures that countries use to regulate markets, protect their consumers, or preserve their natural resources (among other objectives), but they also can be used (or perceived by foreign countries) to discriminate against imports in order to protect domestic industries. TBTs with the greatest impact on agriculture are the various sanitary and phytosanitary (SPS) measures designed to protect humans, animals, and plants, from diseases, pests, and other contaminants. Examples of TBTs, other than SPS measures, are rules for product weight, size, or packaging; ingredient or identity standards; mandatory labeling; shelf-life restrictions; and import testing and certification procedures. The broad term "technical barriers to trade" is frequently applied to all of these types of measures, even where they might be legitimate and consistent with bilateral or multilateral trading rules. However, trade experts widely view TBTs as having great potential for being misused by importing countries as nontransparent (disguised or unclear) obstacles to trade. (See transparency.)