The Federal Aviation Administration is seeking a $12 million fine against Southwest Airlines for what it deems improper repairs on 44 jetliners. It is reportedly the second-largest fine in FAA history.

The federal agency announced its intentions on July 28. Southwest Airlines has 30 days to officially respond to the accusations.

In 2006, Dallas-based Southwest contracted Aviation Technical Services Inc. to work on 44 jetliners in need of repairs. According to the FAA, the contractor did not follow established federal protocol for replacing the fuselage skins to eliminate potential cracking.

The contractor also allegedly failed to properly stabilize the aircraft while the work was being completed. A third component of the fine is related to irregular wiring on two Boeing 737s.

"Southwest returned the jetliners to service and operated them when they were not in compliance with Federal Aviation Regulations," the FAA said in a statement.

For its part, Southwest maintains the issue has already been "fully resolved."

"The FAA letter includes repair issues that were addressed several years ago," Southwest said in a statement. "Having fully resolved the repair issues some time ago, none of the items raised in the FAA letter affect aircraft currently being operated by Southwest Airlines.

"Safety is paramount, and we always strive for full compliance with established and approved processes and procedures."

According to the FAA, the improperly repaired airplanes flew more than 20 passenger flights "after Southwest Airlines became aware of the discrepancies but before the airline corrected the problem."

"The FAA views maintenance very seriously, and it will not hesitate to take action against companies that fail to follow regulations," FAA Administrator Michael Huerta said.

Through a spokesperson, Southwest said it plans to respond to the FAA allegations.