Southwest Airlines has sued its mechanics' union in a bid to halt what it describes as a union effort to disrupt flight operations for the purpose of gaining leverage in contract talks.

The airline's move follows several days during which maintenance issues caused a spike in delayed or cancelled flights.

The Dallas-based airline filed the suit against the Aircraft Mechanics Fraternal Association (AMFA), its national director Bret Oestreich and five union representatives in US District Court for the Northern District of Texas on 28 February.

The suit alleges the union, which represents some 2,400 Southwest mechanics, is carrying out an "intentional and unlawful effort to promote an illegal job action among Southwest's mechanics".

Southwest has asked the court to order the union to halt actions intended to interfere with its operation.

“Today’s action does not alter our dedicated goal of reaching an agreement that benefits our hardworking maintenance employees, nor does it change the company’s unwavering commitment to safety,” Southwest vice-president labour relations Russell McCrady says in a statement responding to questions from FlightGlobal

The union did not immediately respond to a request for comment but denied any organised disruption in a letter last week to Southwest.

The suit alleges the union has encouraged workers to flag aircraft for maintenance work unrelated to flight safety "for the sole purpose of improving [the AMFA's] position in ongoing labour negotiations".

The number of maintenance write-ups for "minor interior" aircraft issues jumped nearly five times after 10 February, Southwest says. More than 60 Southwest aircraft were out of service some days in February, up from an average of 14, says the suit. Southwest operates 752 737s, according to Cirium's Fleets Analyzer.

Southwest's delays and cancellations spiked this month. On 19 February, for instance, the airline cancelled more than 180 flights and delayed some 700 flights, though those figures declined to 58 cancellations and 395 delays on 28 February, according to Cirium data and analytics.

The spike occurred days after union representatives "stormed out" of an 8 February meeting with the airline, says Southwest's suit.

The Southwest Airlines Pilots Association weighed in on the side of mechanics. It issued a statement on 25 February saying Southwest has been "scapegoating" and intimidating mechanics, that the airline suffers from poor management and that the mechanics' union has long complained have having insufficient stocks of parts.

The AMFA and Southwest have been negotiating a new contract since August 2012. They agreed to terms of a new contract in April 2018, but union members voted down the deal.

CORRECTED: An earlier version of this story incorrectly attributed to the AMFA a letter written by Southwest's pilot union. Story also updated to provide comments from Southwest.

Source: Cirium Dashboard