But he said the “divisive rhetoric” coming out of the organization in the wake of the mass shooting earlier this year at Marjory Stoneman Douglas High School in Parkland, Fla., made his decision “crystal clear.”

“At Delta, our values are everything,” Bastian said at Fortune’s CEO Initiative conference in San Francisco on Tuesday. “It’s the culture of the company. It allows us to be who we are.” He said that “the tone of the commentary from the NRA and seeing Delta’s name in the midst of the discussion going on, we just couldn’t be there.”

In fact, Bastian was so certain about the decision that he didn’t give his board a heads up. “The board read about it as everyone else did the next morning,” he said, adding that he “got nothing but support” from his directors.

“If my board had questioned that decision making, they would question me as a CEO,” he said. “I thought it was that black and white.”

Bastian made the decision despite a $40 million tax exemption pending with the Georgia state legislature, which killed the tax break as a result. “We were not going to be moved by it,” he said. “From an investor stand point, the most important asset we have on balance is our culture.” He said that the money actually made it easier, because it became a form of corporate blackmail. “That made it easy for me to justify,” he said.

Bastian said he didn’t even know about what he described as a relatively minor discount program until some of the Parkland students sent him photos of the NRA website promoting the deal, in which NRA members got a discount to fly to organization’s national convention. Only 13 people had signed up for the discount this year.

“The kids said, ‘What are you going to do about it,’” he recalled.

As a result of the incident, Delta has since examined its other partnerships and has ended relationships with about 20 other organizations, which Bastian declined to identify.