Delta Air Lines is rejoining the industry group that represents U.S. airlines, four years after leaving the group over differences on policy issues.

The reuniting resolves a disagreement between the Atlanta-based airline and its industry association that began under former Delta CEO Richard Anderson, a pugnacious leader who took an aggressive and independent approach on policy positions and other matters.

Led by Anderson, Delta in 2015 announced plans to leave industry group Airlines for America (A4A). The association's members include American Airlines, United,  Southwest, JetBlue, Alaska, Hawaiian, Air Canada, UPS, FedEx and Atlas Air.

Delta said then that it would save $5 million in annual dues that could be better used for its own business and to support “what we believe is a more efficient way of communication in Washington on issues that are important to Delta customers and employees.”

The airline at the time said A4A “failed to support Delta on several key issues” including allegations that Gulf carriers unfairly get government subsidies, as well as issues with the Export-Import Bank.

Delta said in October 2015 that it would officially leave A4A effective April 2016.

In the spat, Airlines for America responded that Delta “has not been aligned with other A4A members on a few key industry positions,” including on how to reform the nation’s air traffic control system.

Then A4A, led at the time by American Airlines CEO Doug Parker as board chairman, retorted by giving Delta an “immediate departure” from the association.

The aftermath of the "'I quit!' 'You're fired!'" exchange lasted more than three years after Anderson handed the reins to current CEO Ed Bastian in 2016. Anderson is now CEO of Amtrak.

Bastian in a written statement Wednesday said Delta looks forward to rejoining A4A “and working jointly with other airline members to address issues that impact our people, our customers and the communities we serve.”

Bastian, leading Delta in a growth phase versus the recovery and rebuilding era under Anderson, has taken a different approach on industry issues. Bastian also recently promoted "Delta Kindness Tags" that can be shared with the idea of igniting the idea to "do something kind and make a difference in someone's life."

Delta will officially rejoin A4A in 2020.

Bastian said Delta would work with A4A on issues like sustainability initiatives, fighting certain passenger taxes and advocating for other policies.

A4A CEO Nicholas Calio issued a statement saying the group and its members  are pleased to welcome Delta back,” adding: “We are a stronger association with Delta as a member.”

Calio said the group is more effective “when we speak with a unified industry voice.”

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