A Government Accountability Office report suggests as many as 21,000 people who should never have been allowed into the U.S. got through checkpoints last year.
GAO investigators found some checkpoints unmanned. Guards at others never asked for travel documents.
Customs and Border Patrol say they have to balance commerce with security.
The GAO says CBP needs more front line employees.
The union representing the border agents agrees. The National Treasury Employees Union represents 17,600 officers. And says they have to deal with 400 million people crossing he U.S. border every year. (CNN)