Polls in Iowa and other states show Sanders bunched near the top of the polls with former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren and Pete Buttigieg, the former mayor of South Bend, Indiana.

Warren and Sanders have both long called for expanding the services offered by post offices, especially in rural communities, to include things like banking.

National labor unions wield a great deal of influence in the Democratic primary. Though many have yet to pick sides in the still-crowded 2020 Democratic primary, though the National Nurses United backed Sanders in November, after endorsing him in 2016. Biden's campaign got an earlier boost last year with the endorsement of the International Association of Fire Fighters.

Buttigieg once worked at the high-powered consulting firm McKinsey & Company and has previously released a client list that included the U.S. Postal Service. In 2010, the Postal Service hired McKinsey and other consulting firms and they eventually recommended ways to increase revenue, including cutting back on daily mail service.

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Buttigieg's campaign released a statement in December saying he was “part of a team tasked with generating ideas to increase revenue like selling greeting cards and increasing the use of flat rate boxes.” It added that the candidate “never worked on cost-cutting or anything involving staff reorganization or the privatization of essential post office services.”

In it's statement endorsing Sanders on Thursday, the postal workers' union said that the Trump administration “has released a series of proposals that would end the universal service requirement and also would make significant changes in the pricing structure of mail products." It also noted that there have also been calls to sell the federally run postal service to private corporations.

The union promised to “encourage its members and their families who live and work in all 50 states" to "join Sanders rallies, make individual campaign contributions and volunteer for campaign activities.” It also said it would launch voter registration drives and urge its members, their families and friends to choose “vote by mail” options in states without restrictions on absentee balloting.

