While this pivot comes after a spate of mass shootings, the foundation was laid by activists across the country like Mueller, who’ve spent years applying pressure to stores. Behind the scenes, an army of women has been boycotting shops and signing petitions. The message was loud and clear: They want safety while shopping with their families.

The two major store chains opened a floodgate, and in the days since, Walgreens, CVS, Wegmans, Aldi, Meijer and Publix and others have said they will ask customers not to openly carry guns. The change signals a seismic shift in corporate willingness to engage in the gun debate.

Last week, Kroger, the country’s largest supermarket chain, announced that it would ask customers to stop openly carrying guns in its stores. Its announcement came on the heels of a similar decision by Walmart after a deadly mass shooting at one of its stores in El Paso on Aug. 3.

“I said to him, ‘I’m having a hard time understanding that you will not allow us to deliver a stack of paper through that front door, but you would allow an AR-15 slung over someone’s shoulder,’” Mueller recalled. “He didn’t say anything. And I knew that we had an awful lot of work left to do.”

Mueller, a volunteer for Moms Demand Action , a gun violence prevention organization, wanted to deliver the petitions to the manager. But she was stopped by someone from corporate, she said. He wouldn’t let her into the store, but he did accept her petitions.

A few years ago, Michele Mueller arrived at a Kroger supermarket in downtown Cincinnati, 330,000 signatures in hand, asking the store to stop allowing customers to openly carry guns as they shopped.

Moms Demand Action Michele Mueller, center, and other volunteers for Moms Demand Action took a giant stack of petitions to a Kroger in Cincinnati in 2014 to ask the grocery chain to stop allowing open carry.

“Five years ago, none of these companies were willing to move on this issue,” said Shannon Watts, founder of Moms Demand Action. “It has been the unglamorous heavy lifting of women who have said to them that they won’t shop at their stores until they change their policy.”

When Watts created Moms Demand Action in 2012, she said she realized quickly that shopping was an area where women could be effective at creating change.

“Women are only 20% of lawmakers and 5% of Fortune 1000 CEOs,” she said. “But we make a lot of the spending decisions for families, so that’s a really important lever of power that we have at our disposal.”

According to research by Michael Silverstein, a senior adviser at the Boston Consulting Group and author of “Women Want More: How to Capture Your Share of the World’s Largest, Fastest-Growing Market,” women do nearly 80% of the grocery shopping for their families and make the decisions on purchases in about 72% of consumer spending overall.

“Women have virtual total autonomy in grocery purchasing,” he said. Increasingly, women are doing their shopping online, placing new pressure on retailers to address issues that could cause customers to avoid brick-and-mortar stores.

“Grocery retailers desperately want loyalty, and they want the big weekly shop from the family with young children,” Silverstein said. “Will women switch stores based on their comfort and security? Absolutely. They want a safe, clean environment.”

Shopping Alongside Armed Strangers

One of Moms Demand Action’s first campaigns was to pressure stores to stop allowing customers to openly carry firearms.

Watts said her group zeroed in on open carry because the practice is generally unregulated. The majority of states do not require a background check, permitting or training to openly carry a firearm, she said. Open carry is legal in 45 states, although restrictions vary by state, according to Everytown for Gun Safety.

When a person walks into Kroger or Walmart toting a gun, it can be intimidating and scary for other customers, who cannot identify the intentions of an armed stranger simply by looking at them.

“It shouldn’t be up to women who are doing the shopping to decide whether someone is open carrying or about to open fire,” she said. “We teach children to run from men with guns in schools, and yet we’re supposed to teach them to respect strangers with semiautomatic rifles in a grocery store? It doesn’t make any sense.”

The group’s first target was Starbucks.

In 2013, Watts learned that the chain was going to prohibit smoking within 25 feet of its doors but would still allow customers to openly carry firearms. Smoking was viewed as a public health issue; guns were not.

Volunteers began using the hashtag #SkipStarbucksSaturday, and a few months later, Starbucks announced that guns were no longer welcome. Target and Chipotle soon followed suit.

In 2014, Moms Demand Action launched a national campaign against Kroger, creating a petition asking the store to change its gun policy. (It also launched one against Walmart around the same time.)

Mueller, the volunteer from Ohio, took an active role in organizing the Kroger campaign. She grew up in Cincinnati, where Kroger is headquartered, and was optimistic that the chain would be receptive to changing its gun policy.

She’d spent her entire life shopping there, she told HuffPost. As a kid, she recalled trips to Kroger with her mother as veritable social events, as they would invariably run into someone they knew and get to chatting. As a young wife, Mueller went to Kroger to shop for family meals. And decades later, when her doctor ordered her to cut salt out of her diet, it was at Kroger that she discovered her favorite low-sodium spaghetti sauce, which tasted almost as good as her father’s traditional Italian recipe.

“I’m almost 70, and my entire life, it was like, “Let’s go Krogering,” she said, referring to the store’s advertising jingle. “That song never leaves you if you grew up here.”

In 2014, after Kroger declined to change its policy and would not allow her to hand-deliver the petitions, she stopped shopping there.

Let’s Go Krogering

Twenty-four companies have changed their policies on open carry after campaigns by Moms Demand Action volunteers, Watts said. For the women across the country who’ve been leading the charge, this is a powerful moment.

“That first wave [of wins] that we got felt incredible,” said Norri Leder, a Moms Demand Action volunteer in Texas who worked on the Target campaign in 2014. “And this one feels like the rest of the nation is waking up. It is ludicrous for employees and shoppers to have to determine if someone is a threat to them or not in the current gun violence environment.”

Kaci Churchill, who volunteers for the Arkansas chapter of Moms Demand Action, described a terrifying experience at a Walmart less than a week after a gunman opened fire in a Walmart in El Paso, killing 22 people.