Former vice president Joe Biden speaks to guests at the United Food and Commercial Workers' (UFCW) 2020 presidential candidate forum on October 13, 2019 in Altoona, Iowa.

Another national labor union came off the sidelines Wednesday and endorsed former Vice President Joe Biden in the 2020 Democratic primary.

The International Association of Bridge, Structural and Ornamental Iron Workers backed Biden in the 12-person race for the presidential nomination. In a statement announcing its pick, the 130,000-member union cited Biden's passage of an infrastructure bill in Congress and commitment to ending so-called right to work laws.

"Vice President Biden has proven again and again that he is a friend to union ironworkers," union General President Eric Dean said in a statement. "We need a president who will defend rights and jobs of American workers, and Joe Biden will be that president."

Most U.S. unions have withheld their support in the primary race as candidates hope a push from the key constituency can help them gain ground in a jammed field. The roughly 300,000-member International Association of Firefighters endorsed Biden last year. The more than 150,000-member National Nurses United backed Sen. Bernie Sanders, I-Vt., who has made labor rights a central plank of his campaign.

The Iron Workers union endorsement of Biden comes after two key state organizations threw their support behind Sanders this month. A Communications Workers of America local union that represents nearly 17,000 people in the delegate-rich primary state of California backed the senator on Tuesday. He also got the backing of SEA/SEIU Local 1984, which represents more than 10,000 people in early primary state New Hampshire.

Biden, Sanders and Sen. Elizabeth Warren, D-Mass., have broadly been considered the top contenders for U.S. union endorsements in the race. The national organizations largely lined up behind Hillary Clinton in her 2016 primary against Sanders.

In the 2016 election, President Donald Trump performed better with rank-and-file union members than recent GOP presidential nominees have, according to exit polling data. The president has criticized what he calls "dues sucking" unions and expressed support in the past for right to work laws — which say workers cannot be compelled to join a union as a condition of employment.

The leading 2020 Democratic candidates have promised to fight those laws and make it easier for workers to strike and bargain collectively.

Biden has tried to create distance from Sanders and Warren by arguing the two supporters of a single-payer "Medicare for All" insurance system will jeopardize the health benefits for which unions lobbied. Sanders' labor plan includes a provision requiring companies to pass along savings they get from his system to workers in the form of wages and other benefits.

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