Southwest Airlines and its pilots are at war - now Boeing is caught up in the fight

Southwest Airlines and its pilots union, SWAPA, have been working on a new collective bargaining agreement for nearly half a decade, and it's been tense.

Now, the tension between the airline and the union has reached new heights, with a lawsuit that would effectively ground the airline's incoming fleet of Boeing 737MAX airliners.

With the suit, filed Monday in Federal court, the pilot's union claims the new plane is not included in its current contract. So asking pilots to fly these aircraft are "unlawful tactics" SWAPA alleges.

"Each new type of 737 that has joined the Southwest fleet over the years has required contractual agreement," said SWAPA President's, Captain Jon Weaks, in a statement.

"We believe Southwest Airlines, in planning to fly the MAX without a contract for it, is threatening a breach of status quo under Section 6 of the Railway Labor Act."

"Pilots cannot be forced into labor without a contract in place," Weaks added.

The airline and the union are currently in Federal mediation and have been working on a new agreement since 2012.

Southwest is one Boeing's largest and most important customers, with a fleet of more than 700 Boeing 737 aircraft. The Dallas-based airline is scheduled to be the launch partner for Boeing's next generation 737MAX, set to begin delivery next year.

Southwest currently has a firm order for 200 Boeing 737MAX airliners.

Southwest Airlines and Boeing were not immediately available for comment.