The temporary staffing firm that recruits workers for an Amazon.com warehouse in Pennsylvania's Lehigh Valley is one of the most aggressive firms in the state when it comes to challenging unemployment claims. The seasonal nature of the Seattle e-tailer's business requires it to temporarily double manpower at its warehouse during the holiday shopping season. That volatile employment demand leaves the company susceptible to high unemployment costs since the tax rates businesses pay to support the unemployment system are higher for employers that frequently let workers go. Amazon shelters itself from those higher cost by using a temporary staffing firm. And the staffing firm, Integrity Staffing Solutions, keeps its own costs in check by aggressively fighting claims of former warehouse workers. The result is people who lost their jobs as a result of illness or injury facing challenges when applying for a benefit to which many are entitled.