The 2020 Democratic presidential candidates are uniting behind the 48,000 United Auto Workers who went on strike Monday over a contract dispute with General Motors.

A job is about a lot more than a paycheck. It's about dignity and respect. Proud to stand with @UAW to demand fair wages and benefits for their members. America's workers deserve better. https://t.co/vdYS3sp4eo — Joe Biden (@JoeBiden) September 15, 2019

"A job is about a lot more than a paycheck. It's about dignity and respect. Proud to stand with @UAW to demand fair wages and benefits for their members. America's workers deserve better," former Vice President Joe Biden tweeted early Monday. Biden, a longtime supporter of labor unions, has already won the endorsement of the firefighters union.

The auto workers walked off the job Monday, shutting down 33 manufacturing plants in nine states across the U.S., as well as 22 parts distribution warehouses, when contract negotiations failed after a midnight deadline.

I am proud to support the @UAW workers who are standing up to the greed of GM. Our message to GM is a simple one: End the greed, sit down with the UAW and work out an agreement that treats your workers with the respect and the dignity they deserve. https://t.co/nAQoeX82oz — Bernie Sanders (@BernieSanders) September 15, 2019

Another ardent union ally, Senator Bernie Sanders, sent a message to GM directly: "End the greed, sit down with the UAW and work out an agreement that treats your workers with the respect and the dignity they deserve." Sanders' message throughout his presidential campaign has been one that focuses on lifting up working-class Americans. He laid out a plan last month to strengthen unions, with the goal of doubling union membership in his first term as president.

Auto workers deserve good wages, comprehensive benefits, and economic security. I stand with @UAW as they strike to get what they deserve, and urge GM to come to the table and negotiate in good faith. https://t.co/VRmL7VzSzt — Elizabeth Warren (@ewarren) September 16, 2019

"Auto workers deserve good wages, comprehensive benefits, and economic security. I stand with @UAW as they strike to get what they deserve, and urge GM to come to the table and negotiate in good faith," urged Senator Elizabeth Warren.

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South Bend Indiana Mayor Pete Buttigieg echoed the Massachusetts Democrat, saying GM should "do right by the workers who fuel its profits."

I'm proud to stand with the hardworking members of @UAW in their fight for fair wages, health care, and job security. @GM should do right by the workers who fuel its profits. https://t.co/3XF8OswRRn — Pete Buttigieg (@PeteButtigieg) September 16, 2019

Kamala Harris noted that Americans don't have to be union members to have benefited from organized labor.

"Unions have organized, marched, negotiated, and gone on strike — all to ensure dignity and rights for working people," she tweeted.

The auto workers union has complained that GM has not made much movement over months of talks over the new four-year contract. Workers are demanding fair wages, affordable health care, and better profit sharing. The automaker said it has already made substantial offers, including higher wages, higher profit sharing, health benefits, and $7 billion in factory investments that will create new jobs. GM has also offered an $8,000 payment to each worker once the new contract is ratified.

GM would like to see the auto workers pick up more of their health insurance costs. Currently, auto workers pay about 4% of their insurance costs, while employees at other kinds of companies nationwide pay about 34%.

The auto maker also wants to shrink the wage gap with foreign automakers, who pay about $50 per hour in wages and benefits, compared to GM, which pays about $63 in wages and benefits.

In a statement, GM said that "it is disappointing that the UAW leadership has chosen to strike."

Talks were scheduled to resume at 10 a.m. ET Monday.

While Democrats have encouraged the workers to continue their right to strike, President Trump tweeted that the two parties should just make a deal.

Here we go again with General Motors and the United Auto Workers. Get together and make a deal! — Donald J. Trump (@realDonaldTrump) September 15, 2019

"Here we go again with General Motors and the United Auto Workers. Get together and make a deal!" he urged.

Analysts agree a prolonged walkout could hurt the overall U.S. economy.

This is the first UAW national strike since a two-day walkout in 2007.