Hi Pookie !
I think you should just say that things are changing i have been to lenient with certain thing in my contract and you are going to be referring to the contract much more from hear on in. Even be honest with them and say i can't have the lateness anymore i have a family to feed and a house to clean and when im closed im closed. You just have to do the change and show them you mean business and say enough is enough you can not be late any more. Hope it helps a bit