The US has won a World Trade Organization (WTO) ruling against China's use of tariff-rate quotas (TRQ) for rice, wheat and corn. TRQs are two-level tariffs, with limited imports allowed at the lower 'in-quota' tariff and subsequent imports charged an 'out-of-quota' tariff, which is generally much higher. The US argued that the quotas limited market access for its grain exports.