Late Employee

I have a tech who really knows PCs inside and out, but recently is three to four hours late at least once per week. He is going into his second month working here, and has been late four times. We have flex time in the summer, so right now it isnt really bad, but its usually a Monday AM when lots of people are here. Does anyone have any ideas about what I should do? I can sort of let it slide in the summer, but not at all in the fall.