The International Association of Machinists and Aerospace Workers (IAM) is endorsing Democratic candidate Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE for president, giving the front-runner her second national union endorsement.

“The IAM will not sit on the sidelines while this fight is so clearly underway,” the group's president, Tom Buffenbarger, said in a statement on Friday.

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“Hillary Clinton has been a strong supporter of this union for years and she is now the target of unprecedented attacks, financed on a scale never seen before. The time to help is when help is needed most, and we intend to do just that," he added.

Union leaders endorsed Clinton after 1,700 members chose her from a field of about 20 candidates by margin greater than 2-to-1. She won the backing of nearly half of the members surveyed.

Seventy-one percent of the union's Democratic members supported Clinton, dwarfing the support for other declared and potential candidates, including Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE (I-Vt.) and Vice President Biden.

The Maryland-based union represents nearly 600,000 workers, according to its website.

In general, union workers have pushed Clinton to voice support for a higher federal minimum wage and to oppose a transpacific trade deal the Obama administration is negotiating.

Clinton received the support of another major union, the American Federation of Teachers, in July. Earlier this week, National Nurses United said it was supporting Sanders over her.