Whenever SGX-ST determines that underlying securities previously approved for Option transactions do not meet the then current requirements for continuance of such approval or for any other reason should no longer be approved, SGX-ST shall not open for trading any additional Series of Options covering those underlying securities and any opening purchase transactions in Options of that Series previously opened may be prohibited to the extent that SGX-ST shall deem necessary for the maintenance of a fair and orderly market or for the protection of Purchasers or Writers of Options.