Pulling up the West Bengal government for challenging the Centre's decision to link Aadhaar for giving subsidies, the Supreme Court on Monday wondered how could a state government challenge a law passed by the central government."How can a state government challenge a law passed by the Centre? This way Centre would start challenging the laws passed by the states," observed a bench of Justice A.K. Sikri and Justice Ashok Bhushan.The court also gave time to the West Bengal government to amend its petition questioning the linking of Aadhaar for giving subsidy by the state's Labour Department. The court said West Bengal Chief Minister Mamata Banerjee could challenge the aspect of Aadhaar law requiring linking an "individual" and a "citizen". However, the court gave notice to the Centre on a plea challenging the mandatory linking of mobile phones with Aadhaar. The Centre was given four weeks to respond.