Thornton Hall's success was to come at a commercial price with some local manufacturers quick to copy the designs, and in an era where nearly everyone was a home-sewer, it was a common occurrence for Isabel Harris to see her designs replicated on the street. "I used to have girls come into the Hullabaloo shop with their mum and they would take a garment into the fitting room and get a tape measure out," says Isabel. Eventually the copying got to a point where Isabel and Brian decided to take legal action in a case that made New Zealand law history in 1988. Thornton Hall fought a well-publicised case against Shanton who had blatantly copied a popular dress design of Isabel’s, manufacturing it in cheap material and selling it for a fraction of the price. It was the first copyright case of its kind as no relevant legislation existed at the time. The case was decided in Thornton Hall’s favour and contributed to the creation of the Copyright Act in 1994.