Trai has issued a show cause notice to the Bharti group, offering mobile services under Airtel, for violation of licence conditions by continuing a particular service after the government instruction to stop the service.According to the notice, Sunil Mittal-owned Bharti Cellular informed department of telecom (DoT) that the company provided subscriber local dialing services till January this year even after DoT had instructed all cellular operators to discontinue the service in June 2003.In the subscriber local dialing service, cellular operators permitted their roaming subscribers to be accessed by the local subscribers on a local call basis, which caused a huge loss to BSNL and MTNL.According to sources, the company has sought an extension to reply to Trai's notice."In view of the above facts, Bharti Cellular is called upon to explain why action should not be taken against them for violation of the licence conditions, in particular clause 16.1 of licence agreement for cellular mobile telephony and the licence agreement for unified access services," Trai said in the notice.