Allan Metcalf chose this fake rule as the winner in his competition to see who could come up with the stupidest fake yet convincing prescriptive rule of English:
Because of should not be used to modify a sentence in the future tense, since it is a logical fallacy to impute a cause to something that is not (yet) true. Rather, a construction such as due to or owing to should be used, or the sentence should be rewritten to be more clear.
For example, instead of He's going to Florida next week, because of a friend's wedding, one should write, He's going to Florida next week for a friend's wedding.
Writers who observe this rule thereby uphold an important distinction; a sentence such as Because of the promised bonus, he decided to teach an extra class next summer makes clear that the promised bonus is the cause of the decision (which has already happened), not the cause of the teaching an extra class (which hasn't happened yet, so doesn't yet have a cause).
It is truly a dumb rule. It is clearly and simply written but remarkably difficult to understand. And although it is totally fictive, with a sinking feeling in my heart I see that I can imagine it catching on. For pity's sake, don't let it. It's a joke. See Metcalf's discussion here.