Depends on the RIR that assigned your block. RIPE For example requires you provide a technical reason, AWS gets around this by saying that technically every ins

Depends on the RIR that assigned your block. RIPE For example requires you provide a technical reason, AWS gets around this by saying that technically every instance could have an SSL certificate and thus should have it own IP for compatibility reasons. RIPE will and has reclaimed /24's and /16's from LIRs who didn't follow their guidelines (tl;dr of which is "must be a technical limitation of IP sharing")