The corporation has moved the HC for permission to cut 21,997 mangroves in Thane, Mumbai, and Palghar districts to make way for the project.
Its lawyers said the number of trees to be removed was reduced by more than half from the original target of 53,467.
A division bench of Chief Justice Dipankar Datta and Justice Girish S Kulkarni was hearing plea by the NHSRCL when the NGO, on Monday, raised objections and said the corporation cannot use explosives for construction in the prohibited area.
It said any relaxation ought not to be granted and questioned the lack of any study on survival rate of saplings to be planted as a compensatory measure.