We have a situation where we have been instructed to accelerate works to meet a new milestone date but the Client has specifically noted that the Key Date has not changed (the Key Date is next year and the new milestone is before Christmas this year). In addition, this has not been instructed under Cl 36 "Acceleration" but under Cl 60 "Compensation Events" . As defined under Cl 61.1 we have started the work and issued the quotation and programme to the Client. We have noted that there are a number of works which cannot be achieved (due to issues beyond our control) by the new milestone date and identified all of the necessary risk and mitigation required to achieve the milestone date for the remainder. The problem is that the Client is not accepting the programme and is insisting that we complete all works by the milestone date. In my opinion this constitutes a change under Cl 63.9 "Change to Subcontractors Works Information" and we are considering issuing a response under Cl 18.1 "Illegal & Impossible". We have demonstrated significant good faith and worked at risk for the past four weeks but are now concerned at our level of exposure. Any comments welcome.