National Green Tribunal (NGT) today sought response from the Centre and German automobile firm Volkswagen on a plea seeking a ban on manufacture and sale of its vehicles in the country for allegedly flouting emission norms. A bench headed by NGT Chairperson Justice Swatanter Kumar issued notice to the Ministry of Heavy Industries and Public Enterprises, Ministry of Environment, Forest and Climate Change, Central Pollution Control Board and Volkswagen group, asking them to reply by December 23.Earlier, the government had issued notice to Volkswagen after Automotive Research Association of India found significant variations in on-road emission levels in its diesel models.