As the market continued to nose dive, controlling shareholders and managers who hold more than 5 percent of a company's shares were ordered to not reduce their holdings in the coming six months.
China Securities Regulatory Commission (CSRC) on Wednesday night promised that any disregard of the rule would be "treated seriously".
The measure aims to "maintain stability of the capital market and protect the legal rights and interests of investors," the CSRC said.
The CSRC said that it will clarify what will happen following the six-month sale suspension at a later date.
Chinese stocks continued to tumble Wednesday as investors saw little hope of improvement and opted to panic sell. The benchmark Shanghai Composite Index sank 5.9 percent to finish at 3,507.19 points.
