I thought the court already approved it.
The FISA court has ruled the President has the Constitutional Authority on some individual cases but not the program as a whole so if FISA rules against the administration then it will be hard for them to reconcile their position with the previous rulings. If FISA does rule it unconstitutional then it could be appealed to the SC where even the FISA court could be ruled unconstitutional because it takes a constitutional amendment to strip Constitutional Presidential Authorities.