BEIJING (AP) — China has tightened controls on trading in its yuan in a possible effort to stop a decline against the U.S. dollar that has raised the danger of an outflow of capital from the world's second-largest economy.

Traders must post a 20 percent deposit effective Monday for contracts to buy and sell yuan on a future date. That will raise the cost of betting the currency might fall further, which might help to discourage speculators.

Beijing allowed the yuan to fall by 8 percent against the dollar since early February. That helps Chinese exporters that face U.S. tariff hikes by lowering the price of their goods in dollar terms. But it also could encourage investors to shift money out of China, raising financing costs for companies in the country.