Democratic presidential candidate Elizabeth Warren gestures as she speaks during a campaign stop at George Mason University in Fairfax, Virginia on May 16, 2019.

The Warren campaign did not immediately respond to a request for comment.

"We look to move to the table to come to a bargaining agreement that provides pay and benefits and working conditions that are the best in the nation," Soule said.

Nonmanagement campaign employees authorized International Brotherhood of Electrical Workers Local 2320 to represent them in negotiations with campaign leadership, according to Steven Soule, the local's business manager.

If the effort is recognized, Warren's campaign could be at least the fourth presidential campaign in history to unionize. Sen. Bernie Sanders' presidential campaign employees became the first to secure a union contract when they did so last month.

Also last month, Democratic contender Julian Castro's staff of several dozen unanimously joined the Campaign Workers Guild. The Castro campaign's union contract is still in the works, according to Sawyer Hackett, the campaign's national press secretary.

"No hangups, just a fairly small team trying to pull it together," Hackett wrote in an email.

Rep. Eric Swalwell, D-Calif., who is running for president, has said his staff also unionized.

The Warren campaign's bargaining unit is made up of 208 individuals nationwide, according to Soule. He said that the local had yet to sit down with campaign leadership to begin negotiations. The local conducted an authorization card recognition campaign that received third-party verification on Monday.

Democrats have sought to improve working conditions on their campaigns this cycle. At least half a dozen campaigns signed a pledge vowing to pay interns, the Huffington Post reported last month, and several are taking steps to combat workplace misconduct.

The major candidates are all vying for union support for their electoral bids. So far, only former Vice President Joe Biden has won a major union endorsement, receiving the backing of the International Association of Firefighters in April. President Donald Trump outperformed among union members in 2016 compared with recent Republicans.

Correction: An earlier version misstated the number of presidential campaigns that have unionized. It is at least four.