A UPS truck driver makes deliveries in Northbrook, Ill., on May 10. Nam Y. Huh/Associated Press

Teamsters members at UPS have voted in favor of authorizing a strike if ongoing negotiations fail to reach an agreement.

The vote was 97% in favor, according to the International Brotherhood of Teamsters.

A strike authorization vote is a way for the union to bolster its bargaining position by demonstrating solidarity among members but does not mean a strike is planned against the shipping giant.

“The strongest leverage our members have is their labor and they are prepared to withhold it to ensure UPS acts accordingly,” said Teamsters general president Sean O’Brien in a written statement.

UPS issued a statement saying “The results do not mean a strike is imminent and do not impact our current business operations in any way.”

“We continue to make progress on key issues and remain confident that we will reach an agreement that provides wins for our employees, the Teamsters, our company, and our customers,” UPS said.

While Teamsters members voted to authorize a possible strike, the two sides have made significant progress at the bargaining table.

Earlier this week, the Teamsters said UPS had agreed in contract talks to put air conditioning in new trucks for its drivers, a major resolution of a long-standing battle. On Wednesday, the union said it had already reached tentative agreements on 43 non-economic changes to the UPS agreement.

“This is an extraordinary number of tentative agreements reached and language changed at this stage of negotiations,” O’Brien said. The union plans to submit its full proposal for wages, holidays, and health benefits to UPS negotiators in the next two weeks.

Still, a deadline looms. The UPS-Teamsters contract currently runs through July 31. National negotiations began April 17, and O’Brien has said that if the two sides do not reach an agreement on a contract, Teamsters would go on strike at UPS on Aug. 1.

The Teamsters, with more than 340,000 members at UPS, have the largest private collective bargaining agreement in North America. A strike would cripple shipping across the country, affecting millions of deliveries a day, and damage UPS’s reputation with customers.