In 2013, Janet Sparks and five co-workers went on strike at a Walmart store in Baker, Louisiana. The group rode in a caravan to Bentonville, Arkansas, taking their grievances to the company's shareholder meeting. The experience of walking off the job in protest was exhilarating, but also unnerving.

"It's always a scary thing for a worker to go up against the largest employer in the U.S.," Sparks, 55, said. "There are co-workers around you who are afraid. But we believed in what we were doing."

Three years later, Sparks still believes in what she's doing, even if her path to victory remains unclear. The labor group that orchestrated her strike, OUR Walmart, lost its benefactor last year, when the United Food and Commercial Workers union decided to stop funding the effort. OUR Walmart now faces the same predicament as other non-union groups in the labor movement: How to pay the bills without any dues-paying members.

OUR Walmart is trying to rebuild. This week, it's sending a delegation of workers to Bentonville for Walmart's shareholder meeting. It has a staff of 12 scattered around the country, including several former Walmart employees. Such work requires money, and the group hasn't figured out where it will find that that funding over the long term.

The Fight for $15 campaign in fast food may confront the same dilemma some day, should its main patron, the Service Employees International Union, decide it can no longer afford the investment.

Adrees Latif / Reuters

"We're in this place that's challenging, but also really exciting," said Dan Schlademan, a longtime organizer who co-founded OUR Walmart. "[We're] now a completely free organization, not connected to any single institution. I think we have the freedom now to take what we've learned over the last four years and build on that in ways that might have been harder under the old structure."

OUR Walmart launched in 2011 with the backing of the 1.3 million-member UFCW, a union that's battled Walmart for decades. Walmart is the largest retailer and private-sector employer in the world, with 1.5 million U.S. employees and more than 4,500 U.S. stores. The company is also famously anti-union. The UFCW has never succeeded in unionizing any of Walmart's U.S. workforce.

So the union turned to organizing workers in a less traditional way. Even if it couldn't unionize Walmart workers, the thinking went, the union still had an interest in pressuring Walmart to hike wages, since Walmart sets the tone for the entire brick-and-mortar retail sector. Rather than try to secure a standard union contract, OUR Walmart would pressure the company publicly into raising pay and offering employees better hours and benefits. The model is sometimes called a worker center or "alt labor" -- as in, an alternative to traditional unionism.

Alt-labor groups operate outside the normal parameters of collective bargaining, without recognition by the company or the federal government. They don't have the same power as a union like the UFCW, though they enjoy certain freedoms. (Unlike unions, they don't have to disclose the details of their spending to the government.) But as organized labor's clout has waned -- a mere 6.7 percent of private-sector workers now belong to a union -- alt-labor groups have been effective at making employers squirm and notching victories for workers, particularly in low-wage industries like food and retail. One Florida-based group, the Coalition of Immokalee Workers, shamed major grocers and fast-food companies into signing agreements that improved pay and working conditions for immigrant farm workers in Florida.

OUR Walmart spearheaded strikes and protests that made national headlines around the retailer's Black Friday shopping frenzy. Organizers said hundreds of employees participated in these strikes each year; Walmart insisted the actual figure was much lower. (Schlademan declined to disclose OUR Walmart's membership numbers.) Regardless of who's counting, the strikers comprised a tiny minority of Walmart's massive workforce. But through their courage to walk out publicly, even for just a day, the workers dented Walmart's public image, helping to fuel a growing national debate over income inequality.

"People just took tremendous risks," said Andrea Dehlendorf, another co-founder of the group. "For a long time, nobody really imagined that there would be this kind of movement from within Walmart."

The group apparently succeeded in getting under Walmart's skin. The retailer went so far as to retain the snooping services of Lockheed Martin to deal with the protests, Bloomberg BusinessWeek reported last year. UFCW lawyers filed a slew of charges against Walmart with the the National Labor Relations Board, saying the company illegally retaliated against strikers. Earlier this year, a judge ruled that Walmart broke the law in firing 16 workers and ordered the company to reinstate them. Walmart has appealed.

Without UFCW this could not have been possible. They came and they undergirded us and helped us and taught us. But this was always a separate organization. Janet Sparks, Walmart worker

Walmart implemented some major changes since the strikes began. In 2015, the company announced it would phase in a wage floor of $10 per hour -- nearly $3 per hour more than the federal minimum wage -- in all of its U.S. stores, boosting pay for a half-million workers. After workers said they weren't getting enough hours, the company implemented a program aimed at helping part-time workers convert to full time. It also overhauled its policies for pregnant workers.

Though OUR Walmart and UFCW claim those changes as the result of activism, Walmart said it merely listened to employees and made a strategic investment.

"Remember, this is a $2.7-billion investment in education, training and higher wages to make Walmart a better place to work and shop," Kory Lundberg, a company spokesman, said of the pay hikes. "We’re doing this because we live in a rapidly changing world, and retail today requires new skills to meet the demands of customers who have everything at their fingertips. Walmart will lead by empowering our associates and creating opportunity. As they grow and succeed, so do our customers and so does Walmart."

Lundberg said the company had no comment on OUR Walmart or the UFCW.

Whatever successes the campaign may have had, the latest incarnation of OUR Walmart still needs to figure out how to keep the lights on. A non-union group may help win raises for workers, but it doesn't make dues-paying union members out of them.

It isn't clear how much money UFCW poured into the OUR Walmart campaign. According to the Center for Union Facts, an anti-union group that tracks union spending, the sum can't be determined because the union did not break out spending specifically to OUR Walmart in its disclosure forms. But the financing would have been considerable.

"You see on the one hand they have had an impact, and they have moved the policy agenda," Kent Wong, director of the UCLA Labor Center, said of non-union worker centers generally. "And on the other hand, the issue of their long-term sustainability has not yet been solved."

For some union members and officers, it's hard to justify spending millions of dollars on an endeavor that doesn't directly benefit the union's membership and expand its base. That was apparently the thinking of UFCW's new leadership. After electing a new president last year, the union pulled its funding from OUR Walmart, sending Schlademan and his team packing. The divorce was messy at first, including a dispute over who had the rights to the name OUR Walmart.

Workers affiliated with OUR Walmart said they hope the union and OUR Walmart will reunite their efforts at some point.

"I'm not going to lie and say I'm not saddened by it," said Denise Barlage, an OUR Walmart member who worked at the company's Pico Rivera, California, store for nine years. "They [UFCW] consider us an ally; we consider them one. I believe years down the road, we will get back together. But I feel in retrospect, it might be better for us to be independent."

"The old model has failed several generations ... We should encourage these experiments, but we shouldn't romanticize it. We still haven't figured this out." David Rolf, president of SEIU local 775 and author of "The Fight for Fifteen: The Right Wage for a Working America"

"Without UFCW this could not have been possible," said Sparks. "They came and they undergirded us and helped us and taught us. But this was always a separate organization. I never felt crippled by them pulling out their funding."

UFCW continues its own Walmart campaign, under the name Making Change at Walmart. Jessica Levin, a spokeswoman for the campaign, said the group is currently working with members of OUR Walmart.

"We will always work with those who are truly focused on changing Walmart," Levin said in an email. "We are aggressively reaching out to Walmart workers, as we always have. We always welcome any Walmart worker who wants be part of our national campaign to change Walmart for the better."

The union describes Making Change at Walmart as an effort to keep heat on the company and make it "a more responsible employer." The campaign appears focused less on in-store organizing than on trying to shape Walmart's image through advertising and PR -- a more affordable strategy, for sure, but a less militant one as well.

Levin said the union wouldn't discuss campaign tactics, but was focused on giving workers a voice to "tell their stories, whether that is to groups of Walmart workers, in television or multimedia campaigns, or in front of hundreds of thousands of people at the annual shareholders meeting."

OUR Walmart is searching for funding in its new incarnation. According to Schlademan, the support will be a mix of foundation grants, online donations and contributions from workers themselves. He said the group has secured some foundation money, but declined to name any donors or provide specific numbers.

"Our ability to build a sustainable organization is there," Schlademan said. "We believe this model has the ability to be successful. That is our grand experiment. It's the question we hope to answer."

Other labor groups should hope so, too. The union-backed Fight for $15 came on the heels of OUR Walmart and is funded by the 2 million-member SEIU, which, according to the Center for Union Facts, has devoted tens of millions of dollars to the cause over four years. By most measures, the campaign has been a huge success, spurring minimum wage hikes around the country, including $15 measures in both California and New York.

Yet the Fight for $15 has not yet translated into more dues-paying union members. It's possible that, through public pressure and regulatory channels, SEIU could broker a deal with McDonald's, or other fast-food giants, that paves the way for union contracts. And there's an argument to be made that the Fight for $15 has benefited union workers as well, by helping to raise the baseline pay in the service sector more broadly. But for now, the campaign's most concrete victories are clearly legislative ones. (Fight for $15 members may soon vote to formally affiliate with SEIU, but dues are not yet in the picture.)

Such experiments require investment and patience, said David Rolf, president of SEIU local 775 and the author of a new book about the Fight for $15. Rolf noted that some of the biggest achievements of the U.S. labor movement were years, if not decades, in the making, like the Treaty of Detroit, the groundbreaking contract won by auto workers in 1950. Rolf said unions are more or less doomed within their traditional structure, and must find a new framework for workers to bargain collectively, even if it isn't clear yet how it becomes self-sustaining.

"The old model has failed several generations. It's too inaccessible -- people can't get unions," Rolf said. "We should encourage these experiments, but we shouldn't romanticize it. We still haven't figured this out."

Rick Wilking / Reuters Master of ceremonies for the 2015 Walmart annual meeting, actress Reese Witherspoon, speaks on stage in Fayetteville, Arkansas.

Walmart hosts its annual shareholder meeting on Friday. OUR Walmart has had a presence outside the celebrity-studded confab for several years, and this year is no different. The group plans to deliver a petition calling for a minimum wage of $15, and full, stable work schedules for all employees who want them. UFCW is also in Bentonville this week, hosting a roundtable with workers on Wednesday night.

Sparks earns $13.25 an hour after 10 years at Walmart. She said she'll keep rounding up signatures for the petition, regardless of how much funding OUR Walmart has, or where it comes from.

"It's all looking forward for me. It's about change for Walmart workers and all American workers," Sparks said. "I'm not going to stop because of a few dollars being taken away."