Low farm milk prices and declining dairy farm incomes in 2009 renewed congressional interest in imposing new import barriers on milk protein concentrates (MPCs), which generally include casein, the main protein found in milk, and caseinates, a soluble form of casein. MPCs are derived from raw milk and are used in a variety of food products, animal feed, and industrial products. Currently, U.S. imports of MPCs have limited or no trade restrictions while many other dairy product imports are restricted by tariff-rate quotas. Advocates of stricter import controls on MPCs say they would prevent the unlimited importation of milk protein, which would encourage the use of domestically produced protein and raise milk prices for dairy farmers. Opponents respond that the prospective move would increase their costs and result in higher retail food prices. Major foreign suppliers of MPCs to the U.S. market would likely seek compensation under World Trade Organization (WTO) rules for new U.S. restrictions on MPC imports. Concerns about MPC imports have periodically surfaced since import levels rose sharply in the late 1990s. At that time, the U.S. price of nonfat dry milk, which competes on some level with MPC as a protein ingredient, was above the price for milk proteins in the international market, making the U.S. market an attractive destination. When the world and domestic prices began to converge in 2001, MPC imports dropped off significantly and have since remained at or below peak levels reached in 2000. Milk is comprised mostly of water, measured at 87.4% of total weight. The remaining 12.6% is called "milk solids," which is split four ways: fat (3.7% of total weight), protein (3.4%), lactose or sugar (4.8%), and minerals (0.7%). Milk protein is of two basic types: casein (2.8% of total weight or 82% of total protein) and whey protein (lactalbumin) (0.6% of total weight or 18% of total protein). Casein is extracted from milk by injecting a certain enzyme or acid into skim milk. Historically, casein was used in both industrial applications such as for glue and paper coatings, and in foods, mainly as an ingredient for "nondairy foods" such as imitation cheese, coffee creamers, and margarine. Whey protein is found in liquid whey, which is a by-product of the cheese manufacturing process that must be further processed to retrieve the protein. Whey protein is also used in a variety of food products. A "milk protein concentrate" (MPC) contains both casein and whey protein, and is often identified by its protein content, such as MPC42 for a product with 42% protein. MPCs are manufactured by ultrafiltration (use of membranes to separate larger molecules from smaller molecules in skim milk), blending (combinations of two or more products, such as skim milk powder and casein), or co-precipitation (a procedure similar to casein extraction). Protein concentrates have wide-ranging applications in the food manufacturing industry. Products that contain protein concentrates include infant formula, processed cheese products, imitation cheese, cultured products, frozen desserts, and specialty sports and medical nutrition products. Various protein levels are used in different products: MPC42-MPC56 are generally used in non-standardized cheeses (e.g., brie, ricotta), while MPC70-MPC85 are used in sports drinks and nutritional supplements. MPC90 is used in lactose-free or sugar-free products. Aside from the level of protein, some food manufacturers cite better "functionality" for MPC as an ingredient compared with nonfat dry milk (approximately 35% protein). Some typical functional characteristics include solubility, viscosity, water-binding, whipping and foaming, gelling, and heat stability. Also, processors favor MPC where exact product composition is important or where lactose (present in nonfat dry milk) is not needed or wanted. The United States produces very little casein or milk protein concentrates. Some dairy economists suggest that the federal dairy policies, particularly the Dairy Product Price Support program, have encouraged the production of nonfat dry milk (NDM) at the expense of milk protein concentrate or casein by assuring a buyer (i.e., the government) for NDM. Producers and others counter that foreign subsidies for exports of dairy products have at times limited U.S. production of protein products. U.S. imports of dairy products were valued at just over $3 billion in 2008 as measured by the USDA's Foreign Agricultural Service ( Table 1 ), with cheese accounting for the largest share at 38%. MPCs and casein/caseinates combined represented 35% of total import value. The United States also imports butter, lactose, and a variety of other dairy products such as chocolate milk drinks, pudding, and milk components for food manufacturing. Constraints on dairy product imports are affected by import barriers (see " Import Barriers "), which are needed to maintain the integrity of the domestic dairy program. The U.S. dairy program supports prices of dairy products and pays farmers subsidies when milk prices decline below certain levels. Unlimited market access would leave open the potential for import surges that could result in large purchases by the federal government under the price support program and/or lower farm prices that would drive up payments under the Milk Income Loss Contract (MILC) program. Dairy imports are modest relative to domestic production. The U.S. Department of Agriculture (USDA) estimated import quantities during 2000-2004 at about 3% of milk production, driven primarily by cheese imports. More recent figures indicate little change since then. During most of the last decade, total U.S. imports of MPCs and casein/caseinates have hovered around 150,000 metric tons or less ( Figure 1 ). Since the sharp rise in the late 1990s, there has been no discernible import trend, with a sharp decline in 2009 (reportedly related to weak demand) following a rise in 2008. Primary U.S. suppliers include New Zealand, Australia, and the European Union ( Figure 2 and Figure 3 ). Until 1995, imports of almost all dairy products (butter, cheese, dry milk) were subject to section 22 import quotas. Section 22 of the Agricultural Adjustment Act of 1933 (7 U.S.C. 624(f)) requires the President to impose quantitative limitations or fees on imports that the President finds are being, or are practically certain to be, imported under such conditions and in such quantities as to render or tend to render ineffective, or materially interfere with, any USDA domestic support or stabilization program. Dairy products that were not covered by section 22 quotas included casein, caseinates, whey, and soft-ripened cow's milk cheese (e.g., brie). The 1995 WTO Uruguay Round Agreement on Agriculture converted section 22 quotas (including dairy product quotas) into tariff rate quotas (TRQs). (The United States also agreed to progressive reductions in the quantity and value of export subsidies under the Dairy Export Incentive Program or DEIP.) Importers of dairy products under the low tariff in a TRQ must apply for a license from USDA. No license is required for over-quota imports which are subject to a higher tariff. Since MPCs and casein imports had not been restricted under section 22, they were not subject to TRQs, nor were they subject to licensing requirements. Legislation to implement the WTO Uruguay Round Agriculture Agreement ( P.L. 103-465 ) amended section 22 to prohibit the application of quantitative import limitations or fees on products from other WTO members. Imports of MPCs are classified under the Harmonized Tariff Schedule of the United States (HTS) under subheadings 0404.90.10 for imports with a protein concentration of 40% to 90% and under 3501.10.10 for imports with a protein concentration of 90% or more. Imports of casein and caseinates are classified under subheadings 3501.10.50 and 3501.90.60. MPCs are subject to a very low tariff of 0.37 cents per kilogram. Imports of casein (under 3501.10.50) are duty free; other casein derivatives have a tariff of 0.37 cents per kilogram. During the early 2000s, milk producers and their supporters in Congress tried to change the tariff treatment of MPCs by petitioning the U.S. Customs Service to change the tariff classification of MPCs and by introducing legislation that would have established TRQs for MPCs. In 2002, the U.S. Customs Service (now Customs and Border Protection (CBP)) received a petition from the National Milk Producers Federation (NMPF) to review the tariff classification of MPCs and to change the classification from a non-quota to a quota classification. In its petition, the NMPF contended that dairy products classified under HTS 0404.90.10 did not meet the statutory definition of MPCs and were therefore not classifiable under that subhead of the HTS. They should instead, according to NMPF, be classified under heading 0402 which covers "milk and cream, concentrated or containing added sugar or other sweetening matter." If so classified, MPCs would become subject to TRQs and also in many cases would require import licenses. NMPF contended that to be properly classified as MPCs, a product must have been produced using the process of ultrafiltration and must contain casein and lactalbumin (whey protein) in the same proportion as found in milk. CBP responded, however, that the statutory language (Additional U.S.