Long-standing labor agreements with two major postal unions prohibit the Postal Service from laying off or reassigning workers because of broken equipment or periods of low mail volume. Instead, idled employees show up for work, sit in a break room or cafeteria and do nothing.

Standby time totaled 170,666 hours in the first six months of 2011, costing the Postal Service $4.3 million, according to an audit by the Postal Service inspector general’s office. In 2009, 1.2 million hours were billed at a cost of $30.9 million.

“At a time when the Postal Service is challenged to operate more efficiently, monitoring standby time is critical to ensuring their ability to effectively manage the workforce,” the report said.