The department said in a report that 437,000 checked bags were lost, delayed, damaged or stolen amid new security rules that forced passengers to check bags they might have otherwise taken with them on the plane, USA Today reported Thursday.
The number of incidents was up 33 percent from August 2005 and 74 percent from August 2004. The previous record was 432,000 mishandled bags in December 2004.
David Castelveter, spokesman for the airline trade group Air Transport Association, told the newspaper the number of airline passengers in August was also unusually high, 54.1 million, the third-highest total on record.
Airlines said baggage handing has returned to normal procedures after the government rolled back some security measures last week, but some said their systems still required security upgrades.
"We know we need to make improvements in baggage handling and next year we'll make investments in systems that will help us offer customers better service in this area," Delta Air Lines spokeswoman Betsy Talton told USA Today.