(NewsNation) — The U.S. economy may be facing its largest labor strike in history as negotiations between United Postal Service and the Teamsters Union are set to begin ahead of their current contract’s expiration at the end of July 2023, CNN Business reports.

UPS handles 21.5 million packages a day — the most in the U.S. by far — and transports about 6 percent of U.S. GDP daily.

Should the reported 350,000 Teamsters that work at UPS as drivers and package sorters out of its global workforce of 534,000 permanent employees actually go on strike, it would not only be the largest strike against a single business in the nation’s history but the first strike against UPS since since 1997.

Just last month, newly elected Teamsters President Sean O’Brien addressed UPS in a nationwide call to action, telling the shipping company it “would not have its billion-dollar profits without hardworking Teamster members” and that “it’s time our contract reflects the essential work of our members.”

For Teamsters, that means air conditioning in the back of trucks, better pay packages and improved benefits. This comes after several workers have been injured or died due to extreme heat.

The company has added about 72,000 Teamster-represented jobs since the start of the pandemic and Teamster leaders tell CNN they’re ready to strike now despite the union’s contract with UPS ending in 11 months.

According to CNN, O’Brien says they’ve already collected $300 million in union fees and are prepared to pay members should strike happen sooner.

“Do our members wake up every day wanting a strike? I’d say no. But are they fed up? Yes, they’re fed up,” O’Brien told CNN Business last week. “Whether or not there is a strike, that’s totally up to the company. We’re going to utilize as much leverage as we can to get our members the contract they deserve.”

In response, UPS says it wants a contract “that provides wins for our employees and that provides UPS the flexibility to stay competitive in a rapidly changing industry.”

“UPS and the Teamsters have worked cooperatively for almost 100 years to meet the needs of UPS employees, customers, and the communities where we live and work,” a spokesman told CNN in a statement. “We believe we’ll continue to find common ground with the Teamsters and reach an agreement that’s good for everyone involved.”

The potential strike would likely make the nation’s current supply chain challenges worse.