Sanders' campaign manager Faiz Shakir says the Vermont senator is honored to be the first presidential candidate with a unionized workforce.
The campaign also noted that despite the injury, Sanders proceeded with his scheduled events for the day and will still travel to Nevada for a campaign stop Saturday.
"We can not just support unions with words, we must back it up with actions", he tweeted. On the campaign trail, Sanders has repeatedly vowed in speeches - as he did in 2016 - to make it easier for workers to unionize, often tying it to his push for a rise in the minimum wage to at least $15 an hour.
The United Food & Commercial Workers Local 400 confirmed Friday that Sanders' campaign workers were the first to win union representation.
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He does great work at Northwestern Memorial Hospital in Chicago", the vice president said to applause. "Everything does. Mr Trump said he had seen Mr O'Rourke's announcement and said: "I've never seen so much hand movement".
In January, Sanders apologized to women campaign workers who said they had been harassed or mistreated by male campaign staffers during his 2016 White House bid.
UFCW said Sanders' campaign had agreed to use "card check" to determine whether most workers wanted a union. Sanders' aides said on a recent conference call that the campaign has roughly 70 paid staffers.
Negotiations on a contract are expected to begin soon, the union said, and the bargaining unit could ultimately reach 1,000 members.
Mark Federici, president of Local 400, said in a statement he hoped "this breakthrough serves as a model for other presidential campaigns, as well as party committees and candidates for other offices".