(Bloomberg) -- Southwest Airlines Co., battered by more than a week of flight delays and cancellations from a rash of aircraft maintenance issues, said its investigation has identified a small group of union mechanics that are orchestrating an effort to slow operations.

The airline called on the Aircraft Mechanics Fraternal Association to comply with its legal obligation and “take immediate action to stop this activity,” according to Southwest’s statement late Friday. If AMFA wants to challenge its findings, the carrier said it asked the group to provide information and data so it can work with the company to resolve the "dramatic and highly unusual spike" in aircraft downtime.

An AMFA spokesman declined to immediately comment but said the union is working on a statement.

The disruption that’s caused hundreds of flight delays is the latest eruption of tension between the airline and the union that represents its 2,700 mechanics. Negotiations for a new contract have stretched over more than six years. The airline has taken AMFA to court at least once, and the union twice has called for the firing of airline executives. Southwest has been frustrated in efforts to secure a new contract as it tries to keep costs in check.

Creating Hardship

“We fully respect each mechanic’s right and obligation to identify legitimate safety issues,” the company statement said, echoing a letter sent to the union. “However, the unprecedented increase in out-of-service aircraft over the last few weeks has created a hardship for our employees and customers that must be addressed.”

Southwest said the increased work reports were focused in a handful of maintenance bases.

The Dallas-based airline declared an “operational emergency” on Feb. 15, three days after it began having nearly double the normal number of airplanes pulled from service because of mechanical issues. The carrier told mechanics to show up to work as scheduled or risk losing their jobs. AMFA has said Southwest is attempting to divert attention from safety issues by accusing the union of an illegal work action.

‘Unscheduled Downtime’

The company’s review showed “unscheduled aircraft downtime” increased to 60 hours a day in Orlando from a two-year average of 10.2 hours. The downtime jumped to as much as 127 hours in Houston versus the prior average of 18.6, according to a letter sent to the union. As many as 60 aircraft were out of service in a day, compared with the normal 20.

In a message to employees, Southwest Chief Executive Officer Gary Kelly called the airline’s mechanics “extraordinary” and said they deserve a new contract. Union members in September rejected a tentative agreement that would have provided pay raises and a bonus. Southwest said it would have made them the best compensated mechanics in the U.S. industry.

“For our mechanics’ sake, I would not want these operational issues to delay or obstruct the upcoming March negotiations,” Kelly said. “What we all should desire with a laser focus is a new contract.”

Kelly apologized to employees and customers affected by the flight delays linked to unusual amount of maintenance work.

To contact the reporter on this story: Mary Schlangenstein in Dallas at maryc.s@bloomberg.net

To contact the editors responsible for this story: Brendan Case at bcase4@bloomberg.net, Susan Warren

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