China has told banks to stop giving commissions to real-estate agents for introducing mortgage customers, as Beijing tries to rein in an overheated property market and unscrupulous lending practices. The warning from a banking industry association came after an unexpected decision by the central bank to tighten the reserve requirement for commercial lenders, a move aimed at curbing loan growth amid mounting concerns over inflation and a broad-based asset bubble. The China Banking Association said Wednesday that the new guideline on housing-loan commissions has been in effect since Jan. 1. The association, which is under the directive of China’s banking regulator, didn’t specify whether banks that ignore the guideline would be penalized.