I do believe so. The job is part of your financial aid, so in order to keep that aid, you need to be employed on campus for this year. (americanhistoryquotes confirm?)
Actually, you do not HAVE to work on campus. Barnard does not guarentee jobs to students with Work Study, and it’s actually a little bit harder for students with Barnard College Job awards to find a job than it is for students with Federal Work Study awards. Mostly because students with Federal Work Study awards can apply those off-campus and work for organizations like America Reads (which is what I did my first year).
The job is part of your financial aid, but since YOU get the money, instead of it going towards your tuition, it’s your choice whether or not to try to find a job.
Long story long, when Barnard creates your budget, they include tuition and room and board, but also books, travel and miscellaneous expenses. A lot of the time, they give you that job award to help you pay for the books and other expenses, rather than taking the money and putting it towards tuition.