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Just how much does the U.S. rely on immigrants? Americans are finding out.

In cities across the country, businesses closed their doors on Thursday to show support for the #DayWithoutImmigrants campaign. Spread on social media and messaging apps, the day aimed to make a point about the economic impact immigrants have on the U.S. labor force.

Foreign-born residents of the U.S. were asked to stay home from work or school — and to refrain from shopping. Rallies and marches are taking place in Washington D.C., Chicago and Denver, as well as other cities.

In Staten Island, site of recent #ICERaids, many immigrant-owned stores have shut to join #DayWithoutImmigrants. pic.twitter.com/dbkbeCo7R1 — Daniel Altschuler (@altochulo) February 16, 2017

Celebrity chef José Andrés, who was born in Spain, decided to close most of his eateries Thursday to observe the day.

"It seems immigrants, especially Latinos, it seems we are under attack," said Andrés. "It seems we are part of the American dream, but somehow it seems that America is not recognizing what we are doing."

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The plan for the national "strike" spread over social media with #DayWithoutImmigrants trending on Twitter across the U.S. early Thursday.

Thousands in Chicago march #DayWithoutImmigrants Sign reads: "We are hard workers - not rapists" pic.twitter.com/Cvu8vD0EYl — Teresa Albano (@talbano) February 16, 2017

Some restaurant chains announced plans to close, amid fears that many employees will not show up for work. In California's Bay Area, Chavez Supermarket closed all 10 of its businesses, while in New York's Staten Island the owners of Cafe Con Pon bakeries closed their three locations.

Even at the Pentagon, employees at food concessions including national chains like Sbarro's and Taco Bell said they would not be coming to work.

Saru Jayaraman, co-founder of Restaurant Opportunities Centers United, an advocacy group for restaurant workers, issued a statement supporting the one-day boycott.

"Immigrants are the lifeblood of the restaurant industry," Jayaraman said. "At ROC, we honor the major contributions of immigrants in the restaurant industry — an industry that employs perhaps more immigrants than any other in the U.S. We applaud and support restaurants and workers who, by participating the the Day Without Immigrants, affirm the dignity of workers. Furthermore, we call on all Americans to recognize the influence and importance of immigrants in our communities, economy and daily lives.”

A North Carolina teacher says that majority of his students didn't show up to class on Thursday because of the campaign, which prompted him to share a post on Instagram. The teacher, whose Instagram only identifies him as Claudio said his students are immigrants or come from immigrant families and many decided not to show up in order to show the rest of the U.S. what the country is without them.

"This is what happens when you force people to feel scared. People fight back," Claudio said via Instagram. "Only having 3 out of 54 students, and only having an average of 10 children in each classroom are clear evidence that we are tired of oppression and being belittled."

Hollywood captured a somewhat similar idea in the 2004 film "A Day Without A Mexican," in which all Mexicans in California disappear grinding the state to a halt and wreaking economic havoc. In protest of immigration reform proposals in 2006, a Great American Boycott was also organized for May Day.

From doctors to dishwashers, immigrants are integral to daily life in the U.S. We stand w/ @ChefJoseAndres #ADayWithoutImmigrants. https://t.co/A3gGkCYtLX — Janet Murguía (@JMurguia_NCLR) February 15, 2017

Some social media users, however, suggested that Thursday would be an excellent time for people born in the United States to reclaim the jobs they say that immigrants have taken away.

This is not the first time that advocates for immigrants have tried to point out what they say is their value to the American economy. Advocates say immigrants often do work that other residents of the U.S. do not want to do.

Protesters gather at the Milwaukee County Courthouse during a rally against President Donald Trump's immigration policies on Monday. Darren Hauck / Getty Images

Cheap lettuce, for example, is said by supporters of immigrants to be available because of migrant farm workers. Chicken is affordable in super markets, advocates contend, because Mexicans and other immigrants work in chicken plants, sometimes in undesirable conditions.

The federal government has long acknowledged that a majority of farm workers in U.S. fields are undocumented.

This has been a theme advanced for many years by supporters of immigrants in the U.S., whether documented or undocumented. They contribute to the economy rather than harming it, advocates say.

More than 40 percent of Fortune 500 companies have been founded by immigrants and their children, according to a Partnership for A New American economy.