The Teamsters union said Wednesday that it has demanded that UPS Inc. present its last, best and final contractual offer no later than Friday.

The ratcheting up of hostilities comes one day after the Teamsters gave UPS (NYSE: UPS) one week to submit an economic proposal that was superior to the one the Teamsters called “appalling.”  The company’s initial proposal offered small pay raises and cuts to traditional cost-of-living adjustments, the union said.

A last, best and final offer (LBFO) is a formal offer that one side — usually the employer — submits to the other for an agreement. It is supposed to include all compromises that the offering party is willing to make, but that is not always the case. The LBFO is often submitted to union members for their vote to reject it or accept it.

The Teamsters met with UPS negotiators late into Tuesday night over Article 34 of the union’s National Master Agreement, governing health and welfare and pension benefits for members. Despite early progress, UPS attempted to “move the goalposts at the 11th hour and withhold any additional benefits from the Teamsters, seeking concessionary language instead,” the union said. The Teamsters did not provide any details.

When the Teamsters walked away from the table, UPS agreed to resume negotiations Wednesday. When corporate executives showed up, they only resubmitted the same proposal for worker concessions under Article 34, the union said.

“The largest single-employer strike in American history now appears inevitable,” said Teamsters General President Sean M. O’Brien. “Executives at UPS, some of whom get tens of millions of dollars a year, do not care about the hundreds of thousands of American workers who make this company run. They don’t care about our members’ families. UPS doesn’t want to pay up. Their actions and insults at the bargaining table have proven they are just another corporation that wants to keep all the money at the top. Working people who bust their asses every single day do not matter, not to UPS.”

“Last week, we provided our initial economic proposal. This week we followed with a significantly amended proposal to address key demands from the Teamsters,” UPS said in a statement. Reaching consensus requires time and serious, detailed discussion, but it also requires give-and-take from both sides. “

The current contract expires July 31, and union leaders have warned that they will strike Aug. 1 without a contract. Teamsters nationwide authorized a strike this month by 97% should UPS fail to come to terms on a new contract. The strike authorization vote was expected.

“We have an economy today that is reliant on parcel delivery and no one in the game handles more packages per day or provides better service than Teamsters at UPS. Our members are fighting for a post-pandemic agreement that honors the sacrifices they made to keep this country moving during the last several years,” said Teamsters General Secretary-Treasurer Fred Zuckerman. “Time has run out for UPS to give workers that honorable contract. “