Former Vice President Joe Biden made an appearance on Thursday at a rally for striking grocery store workers in Boston, where he expressed his solidarity with the union members and his anger at corporate America.

Biden, who is widely expected to soon announce a run for the presidency, highlighted his working-class upbringing in Pennsylvania and his disdain for unfair labor practices.

“Wall Street CEOs and bankers did not build America, you built America,” Biden told a crowd of United Food and Commercial Workers International Union gathered outside a Stop & Shop market in the Dorchester neighborhood.

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More than 30,000 UFCW Stop & Shop workers have been on strike since April 11 as they fight the company over what they've called unreasonable contract and benefit cuts.

“This is morally wrong what is going on around the country, and I’m sick of it, and I’ve had enough of it,” Biden said. “We’ve got to stand to together, and we will take back our country.”

While Biden has not officially declared that he plans to challenge President Trump for the White House, recent polling indicates that he is considered one of the front-runners for the Democratic nomination, alongside Sen. Bernie Sanders, I-Vt. A recent poll by Fox News shows that Biden holds a seven-point lead in a head-to-head race against Trump, while Sanders holds a three-point lead over Trump.

Sources close to the former vice president have told Fox News that the launch of a campaign – which would be Biden’s third for the White House – would come after Easter, which is Sunday, and possibly as early as next week. The sources added that a campaign staff was being lined up and Biden advisers were in the process of hiring staff in the early voting primary and caucus states.

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Looking ahead to his re-election campaign, Trump predicted in a tweet earlier this week that he would face either Biden or Sanders in the general election next year.

Sanders is leading a crowded 2020 Democratic presidential field in fundraising so far, raising $18 million.

Winning back working-class voters is of major importance to 2020 Democrats after the party suffered major losses in union-heavy states like Michigan and Pennsylvania in the 2016 election. Biden has already been courting union voters even before he has officially entered the race.

“You are coming back," he told the International Brotherhood of Electrical Workers last week. "We need you back."

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Biden is not the only potential candidate courting union votes: Sanders’ campaign became the first in U.S. history with a unionized workforce, Massachusetts Sen. Elizabeth Warren joined striking Stop & Shop workers on a picket line in New Hampshire last Friday and California Sen. Kamala Harris hired a top Service Employees International Union executive for her campaign and made her first proposal one to raise teacher's pay.

Major union endorsements are likely several months away, especially because the labor movement is treading carefully after complaints that its leadership was too quick to back Hillary Clinton in the 2016 primary over Sanders.

Fox News' Paul Steinhauser and The Associated Press contributed to this report.