One requiring membership card (4)
I believe the answer is:
club
I believe this clue is a double definition.
'one requiring membership' is the first definition.
(eg a private members' club)
'card' is the second definition.
(the clubs are a playing card suit)
(Other definitions for club that I've seen before include "Union - strike" , "beat" , "Kind of weapon or golf stick" , "Weapon; playing card" , "Weapon for an association" .)