Is this discrimination?

Our company offers tuition reimbursement up to $10,000 a year. Four of us (same pay grade/position/ same area of work as in our supervisors report to the same boss) are enrolled in an educational program through the company. We started the program at the same time and take the same cles. When filling out the paper work, our supervisor has to sign off if it is tax exempt or not. The other 3 people's supervisors gave them tax exempt status. My supervisor refuses to write it off as tax exempt stating it it not necessary that I take the cles. One of the questions for tax exempt status is "is this cl required to maintain your current position". I spoke with him about it and he referred me to his boss. His boss said, it is not required for my position to take the cl therefor the reimbursement is taxable. I mentioned about how other bosses were writting it off as tax exempt and I do not think its fair that I am the ONLY one paying taxes on it. He said, it does not matter and he is not looking into other peoples tax status because their supervisors did not bring it to his attention only mine did. Now, I am stuck paying $3400 a year (~34%) out of my pocket in the taxes. Over the course of the program, it will costs me over $10,000. Is it legal for the company to do this?