(Rewrites throughout with gun safety group calling on streaming services to drop NRATV, additional companies cutting ties)
Feb 23 (Reuters) - Some of the biggest names in corporate America are coming under mounting pressure on Friday to cut ties with the National Rifle Association as gun safety activists intensified calls for a boycott in the wake of last week's Florida high school massacre.
The social media-fueled campaign has already led a range of corporations, from a major insurer to three car rental brands, to severe their relationships with the NRA gun rights advocacy group. Amazon.com Inc and other online streaming platforms are facing demands to drop the online video channel NRATV, featuring programming produced by the group.
Moms Demand Action for Gun Sense in America, founded after the December 2012 Newtown, Connecticut, school shooting that killed 20 first-graders, sent letters to Apple Inc , AT&T Inc, Amazon, Alphabet Inc's Google division and Roku Inc on Friday, asking them to drop NRATV from their products.
"We have been just disgusted by NRATV since its beginning," Shannon Watts, the group's founder, said in a phone interview. "It really propagates dangerous misinformation and inflammatory rhetoric. It tries to pit Americans against one another, all in an attempt to further their agenda of selling guns."
The U.S. Constitution's Second Amendment protects the right to bear arms and the NRA argues that stricter gun control would erode individual rights. The NRA has not commented on companies severing ties.
The latest company to distance itself from the NRA was insurer Chubb Ltd, which on Friday said it would stop underwriting a controversial NRA-branded insurance policy for gun owners that covers legal costs in self-defense shootings.
Symantec Corp said on Friday it ended a program with the NRA offering discounts for its LifeLock identity theft product.
Late on Thursday, three rental car brands owned by Enterprise Holdings Inc said they were ending discount programs for NRA members. First National Bank of Omaha also said it would not renew a contract with the organization to issue an NRA-branded Visa card.
About 22 corporations nationwide offer incentives to NRA members, according to ThinkProgress.com, a news site owned by the Center for American Progress Action Fund.
The hashtag #BoycottNRA was the number one trending topic on Twitter on Friday morning, as users took to the website to call for corporations to end gun lobby deals as a boycott against the organization.
The NRA has fiercely opposed restrictions on ownership of firearms, including the type of semi-automatic weapon used in the Parkland, Florida, shooting.
Nikolas Cruz, a former student at Marjory Stoneman Douglas High School, returned to his old school on Feb. 14 and killed 17 people, mostly students, with a legally purchased AR-15 rifle, according to authorities.
Major companies such as FedEx Corp, which offers up to a 26 percent discount for NRA Business Alliance members, and Hertz rental car company, which offers NRA members up to 25 percent off rates, did not immediately respond to a request for comment on whether they would be cutting ties with the organization.
On Thursday, the world's largest asset manager BlackRock Inc, which holds stakes in gun makers Sturm Ruger & Company Inc and American Outdoor Brands Corp, said it would speak with weapons makers and distributors to understand their response to the shooting.
NRATV, which describes itself as "America's Most Patriotic Team on a Mission to Take Back The Truth," features programming that leans heavily on speeches by NRA chief executive Wayne LaPierre and spokeswoman Dana Loesch.
Among the channel's series is "Empower the People," in which "rape survivor and Second Amendment advocate Kimberly Corban" participates in "advance training" in firearms, and Curator's Corner," which shows off guns in the NRA National Firearms Museum in Fairfax, Virginia.
An online campaign using the Twitter hashtag #StopNRAmazon has also begun to pick up steam in recent days, ratcheting up the pressure on Amazon CEO Jeff Bezos to drop the channel. Many of those tweeting are in the entertainment industry.
"Ironic how the zNRA likes to point a finger at what kids watch on TV... while they spew vile rhetoric on NRAtv, streamed on zAmazon and aimed solely at boosting gun sales," wrote screenwriter Randi Mayem Singer.
Moms Demand Action posted an online petition using the hashtag #DumpNRATV. Watts, the Moms Demand Action founder, warned that Friday's letters were only the beginning of a broader pressure campaign if companies refuse to abandon their NRA ties.
"To be affiliated with them, whether you are a company or a lawmaker, it is not going to pay off in the long run," she said. "Doing business with the NRA is clearly bad business."
Angry student survivors of the shooting have confronted politicians from state lawmakers to U.S. President Donald Trump himself, demanding stricter gun control laws like a ban on assault-style rifles to prevent mass shootings.
In response, the NRA and Trump have suggested arming teachers who have received training to deter attackers, a proposal that has been met with skepticism by teachers unions and gun violence experts. (Reporting by Barbara Goldberg in New York; Additional reporting by Gina Cherelus in New York, Arunima Banerjee in Bengaluru; Writing by Joseph Ax; Editing by Frank McGurty and Grant McCool)