Contract negotiations between UPS and Teamsters, one of the country's largest labour unions, fell through on Wednesday, with both sides accusing each other of "walking away" from the negotiating table.

The fallout in talks comes as the existing agreement contract expires on July 31, and union leaders have warned that a strike is imminent without a contract. 

"Around 4 a.m., UPS walked away from the bargaining table after presenting an unacceptable offer to the Teamsters that did not address members' needs," said Sean M. O'Brien, general president at Teamsters, adding that the UPS Teamsters National Negotiating Committee "unanimously rejected the package."

The labour union said following marathon negotiations, "UPS refused to give the Teamsters a last, best, and final offer, telling the union the company had nothing more to give."

"This multibillion-dollar corporation has plenty to give American workers — they just don't want to," O'Brien added. "UPS had a choice to make, and they have clearly chosen to go down the wrong road."

UPS says Teamsters should return to negotiations

Separately, UPS issued a statement saying that Teamsters should return to the negotiating table ahead of the looming contract expiration.

"The Teamsters have stopped negotiating despite historic proposals that build on our industry-leading pay," UPS said. "We have nearly a month left to negotiate. We have not walked away, and the union has a responsibility to remain at the table.

"Refusing to negotiate, especially when the finish line is in sight, creates significant unease among employees and customers and threatens to disrupt the US economy," the world's biggest package courier added, noting that only the non-union competitors benefit from the Teamsters' actions.

"We're proud of what we've put forward in these negotiations, which deliver wins for our people. The Teamsters should return to the table to finalize this deal," UPS said.

The UPS Teamsters contract covers more than 340,000 full- and part-time workers.

Teamsters said in its statement that "no additional negotiations are scheduled."

"The Teamsters have repeatedly made clear that UPS members will not work beyond the expiration of the current contract. In June, rank-and-file UPS Teamsters authorized a strike by an overwhelming 97%," the labour union added.

According to the international shipping and logistics company Pitney Bowes, UPS distributes over 25 million items each day or about 25% of all US parcel volume.

That is around 10 million more packages than it daily delivered in the years prior to the outbreak.