Los Angeles, Calif. (KTLA) - An online petition calling for Southern California-based In-N-Out to put a veggie burger on its menu has received thousands of signatures since being launched a week ago.

The change.org petition, started by the Good Food Institute, asks In-N-Out CEO Lynsi Snyder to put a meatless option on the immensely popular fast-food restaurant's menu.

Currently, fans of the franchise looking for a vegetarian option can order a "grilled cheese," essentially a cheeseburger without the hamburger patty. The petition seeks to add a meat alternative to the menu.

See images of the infamous burger:



7 PHOTOS In-N-Out See Gallery In-N-Out In-N-Out Burger's signature Double-Double cheeseburger and french fries are arranged for a photograph at a restaurant in Costa Mesa, California, U.S., on Wednesday, Feb. 6, 2013. In-N-Out, with almost 280 units in five states, is valued at about $1.1 billion based on the average price-to-earnings, according to the Bloomberg Billionaires Index. Photographer: Patrick T. Fallon/Bloomberg via Getty Images A Double-Double burger and french fries are arranged for a photograph at an In-N-Out Burger restaurant in Costa Mesa, California, U.S., on Wednesday, Feb. 6, 2013. In-N-Out, with almost 280 units in five states, is valued at about $1.1 billion based on the average price-to-earnings, according to the Bloomberg Billionaires Index. Photographer: Patrick T. Fallon/Bloomberg via Getty Images French fries with ketchup are arranged for a photograph at an In-N-Out Burger restaurant in Costa Mesa, California, U.S., on Wednesday, Feb. 6, 2013. In-N-Out, with almost 280 units in five states, is valued at about $1.1 billion based on the average price-to-earnings, according to the Bloomberg Billionaires Index. Photographer: Patrick T. Fallon/Bloomberg via Getty Images WEST HOLLYWOOD, CA - APRIL 17: In-N-Out Burgers are served at the John Varvatos 13th Annual Stuart House benefit presented by Chrysler with Kids' Tent by Hasbro Studios at John Varvatos Boutique on April 17, 2016 in West Hollywood, California. (Photo by Tommaso Boddi/Getty Images for John Varvatos) WEST HOLLYWOOD, CA - APRIL 17: In-N-Out Burgers are served at the John Varvatos 13th Annual Stuart House benefit presented by Chrysler with Kids' Tent by Hasbro Studios at John Varvatos Boutique on April 17, 2016 in West Hollywood, California. (Photo by Tommaso Boddi/Getty Images for John Varvatos) LOS ANGELES, CA - AUGUST 02: An Air Canada Rouge flight is seen above the In-N-Out Burger restaurant Sepulveda Boulevard arriving at Los Angeles International Airport on Saturday, August 02, 2014 in Los Angeles, California. More than 1,500 flights depart and arrive at LAX on a daily basis, ranking it 6th busiest in the world, and 2nd busiest in the United Sates. (Photo by Kent Nishimura/The Denver Post via Getty Images) The used wrapper of an Double-Double burger is arranged for a photograph at an In-N-Out Burger restaurant in Costa Mesa, California, U.S., on Wednesday, Feb. 6, 2013. In-N-Out, with almost 280 units in five states, is valued at about $1.1 billion based on the average price-to-earnings, according to the Bloomberg Billionaires Index. Photographer: Patrick T. Fallon/Bloomberg via Getty Images Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

"In-N-Out has been letting its fans down by failing to serve anything that would satisfy a burger-loving customer who wants a healthy, humane, and sustainable option," the petition states, noting that the restaurant's vegetarian selections consist of fries and a "cheese-slathered bun."

It noted that other national fast-food chains, including Chipotle and Burger King, have gotten "huge returns" after adding vegetarian options to their menus.

"As a company that prides itself on both customer satisfaction and ethical business practices, adding a meat-free option is a no-brainer," the petition reads. "And by making this single addition, In-N-Out would be making a huge statement that it truly cares about its customers' health and the health of the planet."

More than 18,000 people have signed the petition as of late Tuesday morning. Once it has reached the stated goal of 25,000 online signatures, organizers will send it to Snyder.

This isn't the first In-N-Out has been petitioned for a veggie burger option; another online petition on change.org from from four years ago also sought a meat-free alternative to the traditional burger. It received more than 16,500 signatures before it was "closed."

Emily Byrd, a spokeswoman from the Good Food Institute, said their petition has gotten a lot of backlash online.

"We have seen some of the comments, which a lot of them were oddly full of vitriol," she said.

"This is just a suggestion for the menu and something better for the customers."

KTLA's Cindy Von Quednow contributed to this story.

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