If there is no one to back you up on what you know will be a negative impact or event disaster for your project, take some time to do an analysis on what it means to suddenly go a new direction or change a deliverable:

• Create an alternate schedule – the objections may stop at this point as the delivery date is often non negotiable
• Create an alternate budget – likewise, higher cost, or expenses that will hit the books in a different month or quarter
• Create a scope and features comparison –
  • What will be added or deleted?
  • Will there be more QA hours?
  • Help desk calls or extended training time?
  • What downstream activities need to be created/cancelled?
  • Will we be out of compliance, off contract?
• Be sure to get quotes and information from other teams on how this change will affect them.

If you have been planning your project for a few months, there is always some impact to changing those plans.  Make sure everyone is clear on what that impact is, how much it will cost, and what the new timeline will need to become in order to be a success.