A prominent feature of Japan's capitalism consists of families of companies called keiretsu that are linked by crossholdings of stock shares, intra-group financing, and certain coordinating mechanisms. Two types of keiretsu exist: large horizontally organized industrial conglomerates, such as Mitsubishi, Mitsui, and Sumitomo, and vertically integrated manufacturers, such as Toyota, Nippon Steel, and Matsushita Electric. They have become a contentious issue in U.S. trade negotiations with Japan for several reasons.