Notify when Budget Tracked > Planned

We would like to be able to automatically send notification to multiple users when the amount of tracked time on a budget surpasses the amount of planned time.  We have budgets set aside for consulting hours that our partners receive at a flat fee cost.  Hours over the allowed number of hours are billed hourly.  We'd like to receive notification when we cross that point so that we can proactively reach out to our partners and let them know they will be charged for the remainder of the work.