Sources say China's central bank has issued notice to broaden the base of required reserves, to control lending and battle high inflation.

It is said to now include customers' marginal deposits and may drain as much as 900 billion yuan from the banking system in the coming six months. Put simply, that would leave less room for lending. Deposits to be included are what is paid by banks' clients to secure the issuance of bankers' acceptance, letters of guarantee, and letters of credit.

The six biggest banks are to set aside 21.5 percent of deposits to the central bank, starting September 5th. The reported policy change is expected to tackle the highest inflation since 2008.