Story highlights Besides those fired, three people under investigation resigned or retired, the TSA said

Another 15 agency employees were suspended; all affected can appeal the decision

In March, a Hawaii TV station reported that unchecked bags regularly got on planes

The TSA said these security lapses took place during the last four months of 2010

The Transportation Security Administration fired 28 of its employees -- in addition to three who resigned or retired -- following a probe that revealed bags were allowed onto planes at Hawaii's Honolulu International Airport without being properly screened, the agency said Sunday.

Another 15 people were suspended, the TSA reported in a statement.

The moves come after the agency "completed the adjudication process" it had announced in June, months after the allegations first surfaced. All those terminated or suspended "have the right to appeal the decision," according to the TSA.

The firing is believed to be one of, if not the biggest, such action in the agency's history, with officials previously stating that it underscores they will not tolerate employees who compromise security.

In March, Honolulu's KITV 4 News reported that TSA officers assigned to a morning shift regularly allowed checked bags to be loaded onto flights on nine daily departures without being screened for explosives. Sources told the TV station that such lapses occurred for as long as four months and involved thousands of checked bags. CNN confirmed the investigation.

TSA officers are required to screen 100% of all checked bags before they are stored in the cargo holds of passenger aircraft.

In June, agency officials said they did not know exactly how many bags were allowed onto flights without being inspected but said the lapse took place during the last four months of 2010. The TSA said after it became aware of the problem, it took steps to ensure that every bag is properly screened at the airport.

A TSA official said in June that in addition to rank-and-file screeners and some supervisors, the airport's federal security director and assistant federal security director for screening had also received letters proposing that they lose their jobs.

"TSA holds its workforce to the highest ethical standards, and we will not tolerate employees who in any way compromise the security of the traveling public," TSA Administrator John Pistole said then in a statement.

The TSA said it uses closed-circuit TV, random inspections, covert tests and peer and management oversight to check on the integrity of the system.