The airline added that "it continues to support the Second Amendment."
On social media, some customers thanked the airlines for taking a stance against the NRA while others said they would take their business to other airlines. Delta is the second-largest airline behind American Airlines, which does not have such a discount agreement with the NRA, a spokesman said. Southwest also said it does not have an agreement with the NRA.
The NRA called the decision of the companies to cut perks to the NRA "a shameful display of political and civic cowardice.
In time, these brands will be replaced by others who recognize that patriotism and determined commitment to Constitutional freedoms are characteristics of a marketplace they very much want to serve," the NRA added.
United and Delta had offered airfare discounts of between 2 percent and 10 percent, according to the NRA's website.
The decision by the two airlines is more "symbolic" and doesn't cut any meaningful discount, said Henry Harteveldt, a travel-industry expert and founder of the consulting group Atmosphere Research Group. After airlines have gone through waves of large mergers many travelers may not have much choice in alternative carriers.
"You have consolidation," Harteveldt said.