Talks between UPS and the Teamsters have broken down, opening the door to a possible strike that could involve 340,000 workers.

According to CNN, talks broke down between the two parties, with both accusing the other of ending the talks. There are a number of major factors in play, but ultimately economic considerations seem to be the breaking point.

“This multibillion-dollar corporation has plenty to give American workers — they just don’t want to,” said Teamsters President Sean O’Brien. “UPS had a choice to make, and they have clearly chosen to go down the wrong road.”

For its part, UPS said it made the union a “historic offer.”

“We have nearly a month left to negotiate. We have not walked away, and the union has a responsibility to remain at the table,” said the company’s statement. “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. Only our non-union competitors benefit from the Teamsters’ actions.”

Despite the breakdown in talks, the two parties did agree to some major considerations. Specifically, CNN reports that UPS agreed to retrofit its 95,000-strong fleet of vehicles to reduce heat in the cargo area and has also agreed to only buy air-conditioned vehicles from now on.

With talks breaking down and workers voting on whether to strike, the stakes couldn’t be higher for UPS. With an uncertain future, CNN makes the point that UPS could see much of its business and long-term contracts go to competitors, especially non-union FedEx.