The report by the TSA's Aviation Security Advisory Committee said that full employee screening would not "appreciably increase the overall system-wide protection."
Full physical screening of employees also "is incapable of determining a person's motivations, attitudes and capabilities to cause harm, among other limitations."
"No single measure can provide broad-spectrum protection against risks or adversaries," the report said. "Therefore, risk-based, multi-layered security offers the greatest ability to mitigate risks through the application of flexible and unpredictable measures to protect commercial aviation."
The TSA and most airports could not afford 100% employee screening, the report said.
Only two major airports in the U.S. -- Miami and Orlando -- require employees to be screened through metal detectors, a CNN investigation found
earlier this year.
As a result of the report, TSA Secretary Jeh Johnson announced immediate actions, including criminal background checks every two years for all airport aviation workers, screening of airline and airport employees traveling as passengers, reduction of access points to secure areas at all airports and increased random screening of aviation employees.
Johnson requested the TSA study after a Delta Air Lines ramp worker and passenger at Hartsfield-Jackson Atlanta International Airport were arrested in December for allegedly smuggling guns onto flights to New York. Since the incident, the airport has hired private security to check the bags of employees when they show up for work and has increased overall security.
"Immediately following the incident in December 2014, TSA increased the random and unpredictable screening of aviation workers at various airport access points to mitigate potential security vulnerabilities," Johnson said in a statement.
Sen. Charles Schumer called Johnson's announcement "a prompt response and a significant first step to closing the gaping loopholes in airport security, especially with regard to reducing access points and enhancing criminal background checks."
Specifically, the TSA report said employee vetting should be strengthened by "updating the list of disqualifying criminal offenses, instituting continuous activity monitoring through the inclusion of additional Federal Bureau of Investigation (FBI) and DHS data sources, and maintaining a national database of airport employees whose credentials have been revoked for cause."
In addition, the TSA should expand the collection of domestic intelligence, which would include monitoring social media, and expand national reward programs to encourage employees to report security issues, the report said.
"Although there is no perfect security system, the multiple layers -- which can be routinely enhanced or modified -- provide an effective means to secure passengers, employees and facilities," the report said.
It also recommended increased surveillance of employees who work inside baggage rooms and cargo areas. CNN revealed this month
that passengers filed 30,621 claims from 2010 to 2014 for valuables that were missing from luggage.
The TSA report agreed with a 2008 Homeland Security study that found random screening was more cost-effective than mandatory airport employee screening.
The committee that conducted the TSA study consisted of representatives from the TSA, airports, airlines, airline pilots, aviation security and law enforcement.
Rep. John Katko, R-New York and chairman of the House Homeland Security Subcommittee on Transportation Security, said, "As threats to aviation security continue to evolve, it is critical that the Transportation Security Administration, as well as the airport community, are adequately prepared to mitigate insider threats. I look forward to having a meaningful dialogue with airport stakeholders and the TSA on what can be done, going forward, to improve employee vetting and screening for those with access to sensitive and sterile parts of airports."
Rep. Kathleen Rice, D-New York, a ranking member of the Transportation Security Committee, said the report makes it clear that the "TSA must do more to neutralize the insider threat and prevent security breaches like we saw in December."
"Screening every single employee may not be a cure-all solution, but every single employee should come to work every day with reason to expect that they'll face random screening and inspections," she said.
Lauren Stover, security director at Miami International Airport, told CNN, "We support the findings of the committee and agree that there is no single solution in mitigating the insider threat, however we will continue our employee screening program as we believe that physical screening is a critical component to a layered security program."