Accept members carry weapons (4,4)
I believe the answer is:
bear arms
'carry weapons' is the definition.
(I've seen this before)
'accept members' is the wordplay.
'accept' becomes 'bear' ('bear' can be a synonym of 'accept'**).
'members' becomes 'arms' (arm is a kind of member).
'bear'+'arms'='BEAR ARMS'
(Other definitions for bear arms that I've seen before include "Serve as a soldier" , "Carry weapons" , "right for American?" , "Serve in the forces" , "they may be used in a tight squeeze!" .)