Charleston, South Carolina (CNN) Sen. Bernie Sanders' 2020 presidential campaign will be a union shop.

In a statement on Friday, the campaign said it had recognized its staffers' decision to unionize, making it the first major-party presidential campaign to employ a formally organized workforce.

Sanders tweeted that he was "proud" of the historical marker and, taking a page from his stump speech, tied the development to his own pro-union message.

"We cannot just support unions with words, we must back it up with actions," Sanders said. "On this campaign and when we are in the White House, we are going to make it easier for people to join unions, not harder."

The staffers will be represented by the United Food and Commercial Workers Local 400, which said that anyone below the rank of deputy director would be eligible to join the bargaining unit. The campaign voluntarily recognized the group, the union said in a statement, after a majority of 44 eligible employees signed union cards.

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