The one obvious way would be to remove the publishing permission however doing that will also remove the permission to publish.
As per your description, it seems, you just want to remove permission to remove from publishing queue however not block the publishing for the users of that group.
In such a scenario, you can develop a GUI extension which will disable
the option to remove from publishing. In GUI extension you can easily
get current user and from that user you can get group membership:
Now check if user is part of the group mentioned then disable the option to remove from publishing queue.
As suggested by Nuno, other option is to write event system that will trigger on delete of transaction initiated and will throw excpetion to block the operation.