In January 2021, Mary Gundel received a letter from Dollar General’s corporate office congratulating her for being one of the company’s top-performing employees. In honor of her hard work and dedication, the company gave Ms. Gundel a lapel pin that read, “DG: Top 5%.”

“Wear it proudly,” the letter said.

Ms. Gundel did just that, affixing the pin to her black-and-yellow Dollar General uniform, next to her name badge. “I wanted the world to see it,” she said.

Ms. Gundel loved her job managing the Dollar General store in Tampa, Fla. It was fast-paced, unpredictable and even exciting. She especially liked the challenge of calming down belligerent customers and pursuing shoplifters. She earned about $51,000 a year, far more than the median income in Tampa.

But the job had its challenges, too: Delivery trucks that would show up unannounced, leaving boxes piled up in the aisles because there weren’t enough workers to unpack them. Days spent running the store for long stretches by herself because the company allotted only so many hours for other employees to work. Cranky customers complaining about out of stock items.

So on the morning of March 28, in between running the register and putting tags on clothing, Ms. Gundel, 33, propped up her iPhone and hit record.

The result was a six-part critique, “Retail Store Manager Life,” in which Ms. Gundel laid bare the working conditions inside the fast-growing retail chain, with stores that are a common sight in rural areas.

“Me talking out about this is actually kind of bad,” Ms. Gundel said as she looked into her camera. “Technically, I could get into a lot of trouble.”

But she added: “Whatever happens, happens. Something needs to be said, and there needs to be some changes, or they are probably going to end up losing a lot of people.”

Her videos, which she posted on TikTok, went viral, including one that has been viewed 1.8 million times.

And with that, Ms. Gundel was instantly transformed from a loyal lieutenant in Dollar General management into an outspoken dissident who risked her career to describe working conditions familiar to retail employees across the United States.

As Ms. Gundel had predicted, Dollar General soon fired her. She was let go less than a week after posting her first critical video, but not before she inspired other Dollar General store managers, many of them women working in stores in poor areas, to speak out on TikTok.

“I am so tired I can’t even talk,” said one woman, who described herself as a 24-year-old store manager but did not give her name. “Give me my life back.”

“I’ve been so afraid to post this until now,” another unidentified woman said, as she walked viewers through a Dollar General store while discussing how she was forced to work alone because of labor cuts.

“This will be my last day,” she said, citing Ms. Gundel’s videos. “I am not doing this anymore.”

In a statement, Dollar General said: “We provide many avenues for our teams to make their voices heard, including our open-door policy and routine engagement surveys. We use this feedback to help us identify and address concerns, improve our workplace and better serve our employees, customers and communities. We are disappointed any time an employee feels that we have not lived up to these goals and we use those situations as additional opportunities to listen and learn.

“Although we do not agree with all the statements currently being made by Ms. Gundel, we are doing that here.”

Before March 28, Ms. Gundel’s TikTok page was a mix of posts about hair extensions and her recent dental surgery. Now it is a daily digest dedicated to fomenting revolt at a major American company. She’s trying to build what she calls a “movement” of workers who feel overworked and disrespected and is encouraging Dollar General employees to form a union.

Just about every day, Ms. Gundel announces on TikTok a newly “elected spokesperson” — each one a woman who works for Dollar General or worked there recently — from Arkansas, Ohio, Tennessee, West Virginia and other places. These women have been assigned to answer questions and concerns from fellow employees in those states and most are keeping their identities hidden because they worry about losing their jobs.

Social media not only gives workers a platform to vent and connect with one another, it empowers rank-and-file workers like Ms. Gundel to become labor leaders in the postpandemic workplace. Ms. Gundel’s viral videos appeared as Christian Smalls, an Amazon warehouse employee on Staten Island who was derided by the company as “not smart or articulate,” organized the first major union in Amazon history last month.

Ms. Gundel — who often dyes her hair pink and purple and has long painted nails that she uses to slice open packaging at work — has been able to break through, it seems, because other workers see themselves in her.

“Everyone has their breaking point,” she said in a telephone interview. “You can only feel unappreciated for so long.”

Ms. Gundel planned on a long career at Dollar General when she started working in her first store in Georgia three years ago. She has three children, including one who is autistic, and her husband works at a defense contractor. She grew up in Titusville, Fla., near Cape Canaveral. Her mother was a district manager at the Waffle House restaurants. Her grandmother worked in the gift store at the Kennedy Space Center. Ms. Gundel moved to Tampa as a Dollar General store manager in February 2020, just before the pandemic.

The store used to have about 198 hours a week to allocate to a staff of about seven people, she said. But by the end of last month, she had only about 130 hours to allocate, which equated to one full-time employee and one part-time employee fewer than when she started.

With not as many hours to give to her staff, Ms. Gundel often had to operate the store on her own for long stretches, typically working six days and up to 60 hours a week with no overtime pay.

Ms. Gundel’s protest was prompted by a TikTok video posted by a customer complaining about the disheveled state of a Dollar General store. Ms. Gundel had heard these complaints from her own customers. Why are boxes blocking the aisles? Why aren’t the shelves fully stocked?

She understood their frustration. But the blame on employees is misplaced, she said.

“Instead of getting mad at the people working there, trying to handle all of their workload, why don’t you say something to the actual big people in the company?” Ms. Gundel said on TikTok. “Why don’t you demand more from the company so they actually start funding the stores to be able to get all this stuff done?”

Ms. Gundel soon tapped into a network of fellow employees, some of whom had already gone public about challenges at work. They included Crystal McBride, who worked at a Dollar General in Utah and had made a video that showed her store’s dumpster overflowing with trash that people had deposited there.

“Thanks, guys, for adding some more dirty work for me,” Ms. McBride, 37, said in her post.

She said in an interview that Dollar General had fired her earlier this month, and that her manager had warned her about some of her videos. As someone who had walked out of an abusive relationship with “just the clothes on my back” and lost her 11 year-old daughter to cancer in 2018, “I wasn’t afraid of losing my job,” she said. “I was not going to be silenced.”

Neither was Ms. Gundel. As her online following grew, she kept posting more videos, many of them increasingly angry.

She talked about a customer who had pulled a knife on her and a man who had reached into her car in the store parking lot and tried yanking her through the window.

She said the company’s way of avoiding serious issues was to bury them in bureaucracy. “You know what they tell you? ‘Put in a ticket,’” she said.

Ms. Gundel started using the hashtag #PutInATicket, which other TikTok users tagged in their own videos.

On the night of March 29, Ms. Gundel posted a video, saying her boss had called her that day to discuss her videos. He told her to review the company’s social media policy, she said. She told him that she was well aware of the policy.

“I was not specifically told to take my videos down, but it was recommended,” she said in the video. “To save my job and future career and where I want to go.”

She closed her eyes for a moment.

“I had to respectfully decline” to remove the videos, she said. “I feel like it would be against my morals and integrity to do so.”

Ms. Gundel also got a call from one of the senior executives who had sent her the “DG: 5%” pin she had been so proud of. Ms. Gundel insisted on recording the call to protect herself. The executive said she just wanted to talk through Ms. Gundel’s concerns, but didn’t want to be recorded. The call ended politely but quickly.

On April 1, Ms. Gundel reported to work at 6 a.m. “Guess what,” she said in a post from outside the store. “I just got fired.”

She added, “It’s pretty sad that a store manager or anybody has to go viral on a social media site in order to be listened to, in order to get some help in their store.”

Ms. Gundel continues to post videos regularly and recently started driving for Uber and Lyft.

While Ms. Gundel’s unionizing effort may be an uphill effort, some people say she has already had an impact. In one recent TikTok video, a woman shopping at a Dollar General in Florida credited Ms. Gundel with forcing the company to spruce up the store she shops in.

“Look at the refrigerators — everything’s stacked in there,” the woman said as her camera panned the aisles. “They’ve got toilet paper to the roof, y’all.”

“Thank you, Mary, for going viral and holding your ground and standing up to corporate and losing your job, because it wasn’t done in vain,” she said. “I’m proud to go into a Dollar General now, because look at it. Look at it.”