Investors with stakes exceeding 5 percent must maintain their positions, the China Securities Regulatory Commission said in a statement. The rule is intended to guard capital-market stability amid an “unreasonable plunge” in share prices, the CSRC said.

While China has already ordered government-owned institutions to maintain or boost their stock holdings, the CSRC’s directive expands the ban on sales to non-state companies and potentially foreign investors who own major stakes in mainland businesses. China has unveiled new market-boosting measures almost every night over the past 10 days, steps that have so far failed to revive investor confidence. Foreign traders have been selling Chinese shares at a record pace this week in part due concerns over the government’s meddling in markets.

“This is not something would happen in the U.S. or in any other developed market,” said Brian Jacobsen, who helps oversee $250 billion as the chief portfolio strategist at Wells Fargo Funds Management. “It does smell a little bit of desperation. But in China it’s a very unique system and they are taking unique steps to try to stop the drop.”