My employer offered to pay for my MBA, via a bonus after I finish school. I must pay all tuition upfront. My employer says the bonus will be tax free - is that right?

Background:
• I am working towards completing an MBA program
• My employer has offered to reimburse me for tuition in the following manner:
o I pay the entire tuition upfront
o And my employer will reimburse me via a bonus once I complete the program.
• Will this bonus be treated as tax free (my employer believes this to be the case)
• If not: what would have to be done for me to get a tax free reimbursement from my employer for tuition expenses.