Well sorry for confusion. Let me try to clear it up. Yes, I'd say TO BE is the most formal way, and also that this is more of a STATEMENT and a given FACT that this particular thing WILL BE rejected, no two ways about it. If this is the message you intend to give I'd select to be. For this certain statement.
Of being I would say is not wrong, but it does not come across as well, or as certain as TO BE. Say both sentences out loud, I hope you find that TO BE sounds a little more natural, and correct when you pronounce the sentence......???