The recent massacre of 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, resulted in more than a dozen companies severing ties with the National Rifle Association, which has become a lightning rod for backlash in the wake of the shooting.

United Continental Holdings Inc.  (UAL) - Get Report and Delta Air Lines Inc.  (DAL) - Get Report  were two of the most recent companies to cancel special offers to NRA members, joining Avis Budget Group Inc  (CAR) - Get Report , MetLife Inc.  (MET) - Get Report , Hertz Global Holdings Inc.  (HTZ) - Get Report , Symantec Corp.  (SYMC) - Get Report and others.

Public pressure has mounted on the NRA as high school students from Parkland have taken to the airwaves to air their grievances against the organization which lobbies for loose gun control laws.

The NRA has struck back against the companies that have abandoned the organization, saying they "have decided to punish NRA membership in 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 said.

Not every company has succumbed to the pressure, however, as FedEx Corp.   (FDX) - Get Report has refused to reconsider its relationship with the NRA. 

Students from the affected school have taken to Twitter to begin a boycott campaign against the company, leading the New York Times to declare in an Op-ed Monday that "FedEx Hearts the NRA."

FedEx shares were volatile Monday, starting the day off well in the green before dipping slightly into negative territory.

Gun stocks Sturm, Ruger & Co. (RGR) - Get Report and American Outdoor Brands Corp. (AOBC) - Get Report were down 2.2% and 3.45%, respectively.