DALLAS (AP) — The federal government is suing Southwest Airlines Co. after failing to reach a settlement with the carrier over allegations that repairs to dozens of planes didn't meet safety standards.

The Justice Department sued Southwest on Monday in federal district court in Washington state. The lawsuit seeks to enforce $12 million in civil penalties that the Federal Aviation Administration announced in late July.

The government says that starting in 2006 Southwest hired a contractor to make extensive repairs on 44 planes to prevent the aluminum skin from cracking. The FAA says the contractor, Aviation Technical Services Inc. of Everett, Washington, failed to follow proper procedures.

"We dispute the FAA's allegations and look forward to the opportunity to vigorously defend Southwest's record in a court of law," Southwest spokeswoman Brandy King said Monday night.

The Southwest case is the second-largest penalty that the FAA has ever sought against an airline, behind only a $24.2 million case against American Airlines.

Typically, airlines negotiate with the FAA to reduce the penalties. The FAA hit Southwest with $10.2 million in penalties in 2008, and that case was settled a year later for $7.5 million. The government's decision to sue Southwest barely three months after announcing the most recent penalty indicated the wide gap between the two sides.

The most serious allegation in the current case involves replacement of parts of the fuselages on 44 planes. The FAA said Aviation Technical Services workers under Southwest's supervision put sealant under the new skin panels but didn't install all the rivets fast enough for the sealant to be most effective, which could create gaps for moisture to penetrate and cause corrosion.

Dallas-based Southwest returned the planes to service in 2009 and kept flying some of them for months after the FAA warned the airline of the improper repairs, the FAA said. Regulators approved later repairs.