If you are employed with the FU, you can use their corporate discount. For bookings at the counter, you need the BMIS (bank management info system) account number of the FU, it is 3101593. To book online, you can apply (in German) for access, using this form.
The corporate discount only applies to the “Normalpreis”, not to “Sparpreis” or bookings with a discount through a privately owned BahnCard. If you’d like to combine the corporate discount with a BahnCard discount, you can apply for the BahnCard Business, information (in German) on that here.