One of the biggest strikes in US history is brewing at UPS

New York (CNN Business) Over the past year, the nascent labor movements at mighty corporations like Starbucks and Amazon have grabbed national attention. But less well-known is a looming high-stakes clash between one of America's oldest unions and the world's biggest package courier.

Contract negotiations are set to begin in the spring between UPS and the Teamsters Union ahead of their current contract's expiration at the end of July, 2023. Already, before the talks have even started, labor experts are predicting that the drivers and package handlers will go on strike.

"The question is how long it will be," said Todd Vachon, professor of Labor Relations at Rutgers. "The union's president ran and won on taking a more militant approach. Even if they're very close [to a deal], the rank and file will be hungry to take on the company."

If that happens, a strike at UPS would affect nearly every household in the country. An estimated 6% of the nation's gross domestic product is moved in UPS trucks every year. The explosive growth of online retail has made the company and its drivers more crucial than ever to the nation's struggling supply chain. Beyond the company's home deliveries, it also delivers many of the goods found in stores, factories and offices.

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About 350,000 Teamsters work at UPS as drivers and package sorters out of a global workforce of 534,000 permanent employees. And that's growing fast — the company has added some 72,000 Teamster-represented jobs since the start of the pandemic.