From the SU website:
To enhance your university experience, the Students’ Union provides a myriad of services which are maintained through the Dedicated Fees portion of your Student Fees. Dedicated fees are those created by a referendum stating a specific use for the funds collected.
Some of these fees permit students to ‘opt-out’ of them if the student is either philosophically opposed to these fees or cannot afford them.
Please visit the SU website to opt out.