How to restrict Vendor groups in FBL1N

I'm trying to restrict FBL1N to certain vendor groups but I can't seem to find the right object. I'm not sure whether adding F_LFA1_GRP and restricting KTOKK (vendor groups field) will solve the problem. I've checked SU24 for FBL1N and F_LFA1_GRP is not listed (not even as an optional object)