There may be cross-reactivity if you have a sulfa allergy and therefore alternative medications to sulfasalazine should be considered instead.
There are some similarities between 5-ASA and aspirin and therefore there is a concern of possible cross-reactivity
There has been a report of successful use of 5-ASA in a patient with aspirin allergy by first using a test dose
You will have to discuss with your IBD specialist whether to pursue a supervised test dose to assess tolerability or consider desensitization (trying to overcome the allergy by slowly introducing small doses and gradually increasing to full dose)