Consumers in the Bay Area and across the country have committed to boycotting major store chains and avoiding unnecessary purchases for 24 hours today, aiming to show large corporations “who really holds the power.”

Though the boycott could serve as a warning to corporations about how upset people are over economic and political conditions, experts say that creating substantial change would likely take prolonged action.

Initially organized by advocacy group The People’s Union USA, the economic blackout calls on consumers to not make any purchases in-person or online between midnight and 11:59 p.m. today, especially spending money at major retailers such as Amazon, Walmart and Best Buy and on fast food or gas, according to their website. Participants are also asked to avoid using credit or debit cards for non-essential spending.

Social-media users were spreading the word ahead of the action this week, with famed names such as author Stephen King and former U.S. labor secretary Robert Reich urging consumers to keep their wallets and purses closed. Some users referenced the 1950s Montgomery bus boycott and promoted specific actions against certain companies in the weeks to come.

“Corporations and banks only care about their bottom line. If we disrupt the economy for just ONE day, it sends a powerful message,” The People’s Union website reads. “If they don’t listen (they won’t) we make the next blackout longer (we will).”

The instructions add that participants should still buy essentials — food, medicine and emergency supplies — and encourages these purchases to be made at small businesses.

Economic boycotts can be “very effective,” but longer actions tend to draw more attention, said Julian Vogel, an assistant professor of finance at San Jose State University who holds a doctorate in business administration and finance.

“The impact of a one-day boycott is most likely going to be limited, simply because not buying anything (Friday) might also include, for some people, simply buying a little more on Saturday or more on Thursday,” Vogel said. “What is the main benefit of that one-day boycott, I think, is that if there is a height of participation, this can serve as a stark warning that enough people are taking it seriously.”

If the movement were to turn into an extended boycott, Vogel said, companies will have been warned about how many people would participate.

Larry Gerston, professor emeritus of political science at San Jose State University, explained that spreading the boycott across many different companies could make it less effective, adding that it will be difficult to determine its impact.

“If they targeted one company or another company as an example, I think that kind of approach might result in a greater response,” he said, adding that it is the “easier way out” for people to stop shopping at many stores for just one day and swapping the shopping to another day instead.

The People’s Union USA is a movement of people “unionizing to take back control of our economy, government and future of our country,” according to their mission statement. A GoFundMe page raising money for the organization’s mission had raised more than $70,000 as of Thursday.

John Schwarz, the founder of The People’s Union USA, encouraged people to “hold the line” and not be discouraged if they see people shopping on Friday in a video posted to his Instagram.

“There are 340 million people in America, and not all of them will stand with us, but millions will,” he said. “Make no mistake. We are already making an impact.

“We the people are the economy. Without us, nothing moves. Without us, there is no profit,” he added. “We hit them where they hurts, and that is their wallets.”

Vogel added that more impactful boycotts often have specific asks as opposed to Friday’s general message of economic power. He said the planned boycott has a clear aim at high prices but serves primarily as a warning of the consumer’s strength in the longer-term.

“It helps to know what we’re arguing about,” he said. “I think the messaging for (today) is clear enough that change would theoretically be possible. But again, the one day (boycott) is more like a warning.”

Vogel said it is difficult to find the measurable impact of a boycott, as it would look different for corporations with different operating cycles. The most impactful timeline would be to boycott a company for an entire season, such as refusing to buy everything a company produces for the spring season — from decorations to spring chocolates.

“If they didn’t know how long this was going to last, and we’re a week or two weeks in but there is no telling how long this will go on, then this would definitely have a huge effect,” Vogel added.

Economic boycotts such as Friday’s planned action derive from a combination of emotional factors like frustration and anger and non-emotional factors such as financial hardship, Vogel said.

“I understand the cost, I understand the importance, I understand the frustration that a lot of people have over these incredible changes that are happening right before us and the fact that some people want to do something, but there’s no easy way out here,” Gerston added. “Things have to be structured in a way where they really make a difference.”

The first month or so of President Donald Trump’s term people have largely “sat back,” Gerston said, but he is beginning to see wider reactions to some of the new administration’s executive orders and policies. These movements will likely develop into larger protests over the next few months, but they often take a while, he said, adding that protest movements are often “herky-jerky.”

“You take a step forward, you take a step backward,” he said. “Some fall apart. Some gather steam. These things, ultimately if they’re going to succeed, have to succeed over time.”