The Bhopal bench of the National Green Tribunal (NGT) has issued notices to the collectors of four major districts in Madhya Pradesh, seeking their replies on the contempt plea, which alleged that they did not ensure compliance with the tribunal's previous order as people at these places burst firecrackers during Diwali last year, leading to rise in air pollution. In the order, NGT's judicial member Shivkumar Singh and member expert Arun Kumar Verma on Friday directed the collectors of Bhopal, Indore, Jabalpur and Gwalior to file their replies within four weeks, the petitioners' counsel Prabhat Yadav told PTI on Saturday.