A growing number of US companies have cut ties with the National Rifle Association (NRA) as the gun lobby comes under immense criticism following the last week's mass shooting at a Florida high school.

Several car rental companies, hotels and banks have cancelled the special offers and discounts they have for NRA members.

On Saturday, Delta Air Lines and United Airlines became the latest companies to join the list.

The moves come amid widespread calls to boycott companies and groups that have ties to the powerful pro-gun group.

At least 17 people were killed last week when a gunman opened fire on students and teachers at the Marjory Stoneman Douglas High School in Parkland, Florida. According to police, 19-year-old Nikolas Cruz confessed to carrying out the shooting. He allegedly used an AR-15-style semiautomatic rifle.

Since the shooting, students and their families have organised near-daily protests, demanding gun control reform. Online, the #BoycottNRA campaign has gained momentum, with many pledging to stop doing business with companies that have ties to the NRA.

Under pressure, more than a dozen companies - including car rental giants Hertz and Budget, First National Bank and MetLife insurance - have ended their relationships with the NRA, according to progressive news site ThinkProgess.

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Car rental company Enterprise said on Twitter that discounts for NRA members would no longer be effective starting March 26.

Thank you for contacting us! All three of our brands have ended the discount for NRA members. This change will be effective March 26. Thank you again for reaching out. Kind regards, Michael — EnterpriseRentACar (@enterprisecares) February 23, 2018

We have notified the NRA that we are ending the NRA's rental car discount program with Hertz. — Hertz (@Hertz) February 23, 2018

First National Bank of Omaha, the largest privately held bank in the United States, said it would not renew its contract with the NRA. As a result, the bank will stop issuing NRA credit cards.

Customer feedback has caused us to review our relationship with the NRA. As a result, First National Bank of Omaha will not renew its contract with the National Rifle Association to issue the NRA Visa Card. — First National Bank (@FNBOmaha) February 22, 2018

Insurance company MetLife and software company Symantec, known for the Norton antivirus program, also announced the cancellation of their NRA member discounts.

We value all our customers but have decided to end our discount program with the NRA. — MetLife (@MetLife) February 23, 2018

Symantec has stopped its discount program with the National Rifle Association. — Symantec (@symantec) February 23, 2018

This week, NRA Executive Vice President Wayne LaPierre called on "every citizen who loves this country and treasures its freedom to stand and unflinchingly defend the Second Amendment, the one freedom that protects us all."

"I call on every citizen who loves this country and treasures its freedom to

stand and unflinchingly defend the Second Amendment, the one freedom

that protects us all." - Wayne LaPierre @CPAC 👏 👏 👏 — NRA (@NRA) February 22, 2018

LaPierre was speaking to participants of the Conservative Political Action Conference (CPAC), an annual politically conservative conference.

During that same conference, US President Donald Trump reiterated his proposal to arm teachers who are "adept at firearms" in an effort to stop school shootings.

"Out of your teaching population, you have 10 percent, 20 percent, very gun adept people", Trump said.

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"So this crazy man, who walked in, wouldn't even know who it is that has it," he added. "That's good. That's not bad. That's good. And the teacher would have shot the hell out of him before he knew what happened."

The proposal has been slammed by survivors of mass shootings and their families, as well as a number of teachers, who say having guns in the classroom will only create more problems.

On Friday, the investigation into the shooting revealed that an armed deputy was present at Marjory Stoneman Douglas High School during the incident. According to Sheriff Scott Israel, the deputy waited outside the school for nearly four minutes while the shooting took place. That deputy has since resigned.