Players Getting Gamemode with mod?

[wazzUPP11]

Hello, I have my tekkit classic server at and recently many players have come on and are able to get gamemode because of a client they have. I found a plugin to make all tekkit items spawned in creative turn in to dirt unless you have a proper permission (given to moderators and above). This was working well until players just came on and started spawning MC items like MANY stacks of diamond blocks and just giving hand outs. Any way to stop this mod or to make ALL items turn to dirt to those without permission? thanks