The Supreme Court on Saturday refused to give more time to taxi operators in the National Capital Region (NCR) to switch from diesel to the cleaner compressed natural gas (CNG).The deadline for the change, which has been extended twice, is Saturday.A number of cab operators and their associations urged the court for an extension of the deadline, but a bench comprising Chief Justice T.S. Thakur, Justice A.K. Sikri and Justice R. Banumati refused the request.The apex court had initially asked the diesel cab operators in the NCR to switch over to CNG by March 1. That deadline was later extended to March 31 and then to April 30.The matter related to steps to be taken to curb alarming increase in air pollution in the national capital.