Excerpt from the Berlin Higher Education Act (§18a)
(1) The tasks of the student body shall also include agreeing on low-cost use of public transport for students at universities in accordance with § 1 paragraph 1 as well as other state or state-recognised universities (semester ticket). Participation in the introduction of the Semester Ticket is agreed for each university by the General Student Committee with the contract partner responsible according to § 4 of the Public Transport Act of 27 June 1995 (GVBl. S. 390).
(2) The agreement requires the approval of the students of the respective university. The voting in favour shall be deemed to have taken place if a majority of the participants in a ballot or other survey conducted by the student body of the respective higher education institution, but at least ten per cent of the registered students of the higher education institution, have voted in favour of the introduction. The General Student Committees shall be responsible for concluding the contracts.
(3) Students who are unable to use the semester ticket for health reasons or due to absence from the university for study reasons shall be exempted from the obligation to participate upon application.
(4) In order to fulfil their obligations under the agreements referred to in paragraph 1, the student bodies shall, in accordance with a statute, levy contributions from all students of the participating universities who are not exempted in accordance with paragraph 3, which shall be shown separately from the contributions in accordance with § 20 and shall not require the approval of the university management. They are due for each semester upon matriculation or re-registration and are collected by the universities free of charge. The student bodies shall make use of the institutions of higher education administration in accordance with § 20 paragraph 2 for the administration and management of the fees and any management profits and shall conclude administrative agreements with the higher education institutions for this purpose, in which several student bodies and several higher education institutions may also be involved. If an administrative agreement is not concluded, the Studentenwerk shall be responsible for the administration and management of the fees and any management profits in return for reimbursement of costs and in accordance with the requirements of the student body.
(5) The student bodies may stipulate by statute that a surcharge must be made on the semester ticket fee and that students may be granted a discount on the ticket price in accordance with the funds available in the event of particular social hardship. The statutes require the approval of the university management; otherwise paragraph 4 shall apply accordingly.
(In the following links in german, no translation available.)
For more information on the semester ticket, see also the LandesAstenKonferenz.