As in 'it is due to the fact' : generally careful users of English avoid using due to as a preposition (i.e. before the noun to which it refers) in the written form. Because of is nearly always preferred. Some users believe that due to should be restricted to its monetary meaning.
When the due of due to is clearly an adjective ("absences due to the flu"), no one complains about the phrase. When due to is used as a preposition ("Due to the holiday, our office will be closed"), some people object, so in formal writing an alternative such as because of or owing to may be safer.
Due to should be used to mean "because of " only after a form of the verb be:Darla left the house because of [not due to] her husband's violence. Freida's success was due to hard work.