(a)   Written objections to plan confirmation by parties other than the chapter 13 trustee shall be filed and served on the trustee, the debtor and debtor's counsel at least fifteen days before the scheduled confirmation hearing. The court may refuse to consider an objection that is not filed and served timely, or impose other appropriate sanctions.
 
(b)   The chapter 13 trustee may file written objections to confirmation at any time before the confirmation hearing and also may object orally at the confirmation hearing.