"Massive surcharges" refers to significantly high additional fees or extra costs imposed on top of the original price for a particular product or service. Full definition
Book European awards using British Airways miles — you'll be hit with massive surcharges on BA flights, which all go through London and are heavily taxed; even on partners such as American there will be high fees (travelsort.com)
Of course, you could also use Korean Air SkyPass miles to book Emirates award tickets, but they also hit you with massive surcharges. (straighttothepoints.co)
Delta has done all sorts of either mistakes or tests recently, like increasing taxes on Ex-US awards to Europe to include massive surcharges only to roll those back a few days later. (milestalk.com)