The guard comes from a culture and surroundings where chewing of tobacco is common.
Take an advisory role and insist that tobacco chewing is injurious to health and pollutes the area by spitting and throwing plastic covers etc.
Talk to owner and tell him that factory rules do not permit smoking/chewing tobacco etc and guards should be sensitised to this requirement.
First time you see such a thing,there is no need to terminate.
Vendors during selection process itself should be sensitised about these policies in the factory area.
During supervisory rounds,meetigs this point should be noted and spoken about.
After serious efforts are made, then only defaulters need to be punished.