New setting factionMemberLimit (default 0, no limit), which will prevent players from joining any faction that has reached this membership limit.

src/com/massivecraft/factions/Conf.java

@@ -40,6 +40,9 @@ public class Conf
 	
 	public static boolean newFactionsDefaultOpen = false;
 
+	// when faction membership hits this limit, players will no longer be able to join using /f join; default is 0, no limit
+	public static int factionMemberLimit = 0;
+
 	// what faction ID to start new players in when they first join the server; default is 0, "no faction"
 	public static String newPlayerStartingFactionID = "0";
 

src/com/massivecraft/factions/cmd/CmdJoin.java

@@ -42,6 +42,12 @@ public class CmdJoin extends FCommand
 			return;
 		}
 
+		if (Conf.factionMemberLimit > 0 && faction.getFPlayers().size() >= Conf.factionMemberLimit)
+		{
+			msg("<b>The faction %s is at the limit of %d members, so you cannot currently join.", faction.getTag(fme));
+			return;
+		}
+
 		if (fme.hasFaction())
 		{
 			msg("<b>You must leave your current faction first.");