Students from countries that are not members of the European Union (so-called "third countries") as well as Romania and Bulgaria require a work permit for employment in Austria.
Work permits may be obtained, for students who have completed the first half of their diploma study, for employment up to 10 hours / week, or, after completion of a Bachelor degree, for up to 20 hours / week.
This work permit must be requested from the Public Employment Service ("Arbeitsmarktservice") by the employer. More exact information can be found at the following link: http://www.migration.gv.at/en/types-of-immigration/permanent-immigration-red-white-red-card/students-and-graduates.html
Because this regulation is relatively new and therefore not known to some employers, we recommend that you refer to the above Internet website when applying for a job.