Allowing private contractors to decide who can access secure or restricted areas of seaports and airports poses a security threat, says a report by the U.S. Government Accountability Office.

The report issued in July is coupled with a letter from U.S. Rep. Bennie Thompson, D-Miss., ranking member of the House Committee on Homeland Security. It states the government ultimately fails to do proper background checks on these people, who are eventually allowed to handle hazardous materials.

The Transportation Security Administration has an adjudication center, created in 2005, which hires contractors who then screen the potential workers. The approved workers gain credentials for 12 TSA programs, "including the Transportation Worker Identification Credential (TWIC) program for maritime workers, Hazardous Materials Endorsement (HME) program for commercially licensed drivers, and the Aviation Worker program," according to the report.

Since 2003, TSA says it has vetted around 15 million applicants who have gone on to work in 450 airports and about 360 seaports, according to the report.

Problems with the adjudication center date back to December 2011, when GAO reported the center didn't have enough employees to handle its workload accurately. The 2011 report says "excessive risk exists by allowing contractors to make security credential approvals without sufficient federal oversight."

Adding to the risk, GAO also reports that the adjudication center uses a "cumbersome, manual process to track case production and performance" of its contractors.

In May 2012, TSA said it was working on fixing those issues, but GAO now finds that repair plan outdated and delayed.

The Department of Homeland Security agreed with all five recommendations given by GAO, which says it will monitor Homeland Security's efforts.