Salt-and-iron commissioners (yantieshi 鹽鐵使) were entrusted with the supervision of goods whose production and marketization was subject to a state monopoly. Apart from salt and iron or other metals (silver, copper, lead, tin), tea, alum and ferments belonged to the monopolized commodities.
The office was created during the Tang period 唐 (618-907) and was for some time merged with that of transport commissioners (zhuanyunshi 轉運使) to the salt-and-iron and transport commissioners (yantie zhuanyun shi 鹽鐵轉運使). The salt monopoly played only a minor role in the early Tang period, but in 713 Jiang Shidu 姜師度 submitted a memorial to the throne with the request to establish a salt colony (yantun 鹽屯) at the salt lake of Anyi 安邑 (today's Yuncheng 運城, Shanxi). The monopolized sale of the salt produced in this place yielded substantial profits to the government, and therefore, in the same year, Liu Tong 劉彤 suggested to monopolize the profits of all products of "the mountains and lakes" (shan ze zhi li 山澤之利). Jiang Shidu and Qiang Xun 強循 were both appointed Palace Aides to the Censor-in-chief (yushi zhongcheng 御史中丞) and dispatched as commissioners to check the potential of levies from such an expanded state monopoly. The structure of the salt colonies was similar to that of military agro-colonies (tuntian 屯田), where peasants were obliged to work in the salterns, or wealthy families encourage to invest. Each of these small "enterprises" was taxed according to a defined quota. The salt colonies were administered by local officials.
With the outbreak of the the rebellion of An Lushan 安祿山, military expenditure increased dramatically. In 758 threfore, Diwu Qi 第五琦 was appointed Director of the Tax Bureau (duzhi langzhong 度支郎中) and concurrently Palace Aide to the Censor-in-chief and entrusted with the supervision of the salt-and-iron commissioners in all circuits (dao 道) of the empire. Diwu Qi took care for the formulation of rules on the organization of the monopoly. In salt-producing places, salt households (tinghu 亭戶, zaohu 灶竈, 竈戶) were commissioned to boil salt. It was sold at a price of 10 qian 錢 (coins, see money) per dou 斗 (see weights and measures) of salt, yet the government claimed the right of purchasing the full output. The government then distributed the salt to all circuits via touring brokerages (xunyuan 巡院) and sold it at a price of up to 110 qian per dou. Private production and smuggling of salt was strictly forbidden. The revenue from the salt monopoly (the salt tax yanke 鹽課) constituted the larger part of the state income in the second half of the Tang period.
In 760, when the reformer Liu An 劉晏 was salt-and-iron commissioner, he introduced a new method to cut cost. The government sold the salt at a high price to merchants, who were ordered to transport it to its destination, be it prefectures within the empire, or border garrisons in the north. In very remote places of southern China, salt storehouses (changping yancang 常平鹽倉) were built to ensure that the salt price was stable when less salt arrived. In the salt-producing areas of the Huai River region supervisors controlled the production, storage and sales of salt, and took care that no one engaged in illicite production or trade. Before Liu Yan's reforms were carried out the annual revenue from the salt monopoly was about 400,000 min 緡 (strings of 1,000 cash coins), yet in 780 it had increased to more than 6 million, which was about half of the whole state revenue during that time. The distribution of salt was also supervised by the transport commissioners, so that the two offices were closely connected to each other, and often merged in personal union.
Mining products were in the early Tang period still privately produced, but local governments claimed the right of buying the full output of mines. In 727 silver and tin was for the first time taxed, and all mining products fell under the jurisdiction of the authorities during the reign of Emperor Dezong 唐德宗 (r. 779-804). Vice Minister of Revenue (hubu shilang 戶部侍郎) Han Hui 韓回 arranged for the full purchase and distribution of mining products by salt-and-iron commissioners. In 836 the monopoly fell back to the prefectures, but Emperor Xuanzong 唐宣宗 (r. 846-859) laid organization and revenues back into the hands of commissioners, even if the tax volume earned from mining products was far less than from the salt business. It amounted to 70,000 min per year, which was even less than the revenue from the tea tax of one single district. In some cases salt-and-iron commissioners were entrusted with the production of copper cash. They were then concurrently called coinage commissioners (zhuqianshi 鑄錢使).
Tea was first taxed by a state monopoly in 783. Ten years later commissioner Zhang Pang 張滂 laid out rules for the administration of the tea monopoly. From each harvest, ten per cent were levied, which led to an annual revenue of 400,000 min. During the reign of Emperor Muzong 唐穆宗 (r. 820-824) commissioner Wang Bo 王播 suggested to raise the levy to fifty per cent. In 835, when the Counsellor-in-chief (zaixiang 宰相) Wang Ya 王涯 was concurrently salt-and-iron commissioner, he introduced the tea taxation law (quechafa 榷茶法), according to which tea farmers were ordered to transplant their tea bushes to government-owned tea farms, where the monopoly was better to control. Tea leaves harvested and already processed before the transplantation were all burnt. These measures were controlled by *tea tax commissioners (quechashi 榷茶使). Tea farmers revolted against this law, so that Wang's successor Linghu Chu 令狐楚 abolished the law.
The office of salt-and-iron commissioner was a highly important one and always occupied by trustworthy officials with high credits (like Counsellor-in-chief, or military commissioner) in personal union. The high revenues controlled by the commissioners made it necessary that in the later decades of the Tang period the offices was closely connected to the agencies of the Ministry of Revenue (hubu 戶部). In 930 the office was even merged with that of the Tax Bureau commissioner (duzhishi 度支使) and the Census Bureau commissioner (hubushi 戶部使), and was in 1003 called commissioner of the Three Fiscal Agencies (sansishi 三司使). Song period 宋 (960-1279) salt-and-iron commissioners also regulated the transit tax, markets, canals, and the military equipment of garrisons.