The China Iron and Steel Association (CISA) has asked steel companies and traders with import licenses to boycott iron ore from Vale (VALE.NYSE), Rio Tinto (RIO.ASX, RIO.LSE, RTP.NYSE) and BHP Billiton (BHP.ASX, BLT.LSE, BHP.NYSE) to protest a "monopoly in the iron ore market," state media reported. CISA Director Shan Shanghua asked that mills and traders boycott the miners for two months after the April 1 deadline for iron ore price negotiations between Chinese mills and foreign suppliers passed without an agreement. China has been seeking price discounts within the current annual pricing framework, but suppliers have been pushing for changes that would include market-based pricing mechanisms.