The Teamsters local unions, which represent 340,000 workers at United Parcel Service, voted 161-1 on Monday to endorse the tentative agreement reached with the delivery giant on July 25.
The agreement, estimated to be at $30 billion by the union, provides historic wage increases, one more paid holiday and air conditioning in the company's ubiquitous brown delivery trucks.
It also eliminates a two-tier pay system and forced overtime for delivery drivers.
"Our tentative agreement is richer, stronger, and more far-reaching than any settlement ever negotiated in the history of American organized labor," said Teamsters General President Sean M. O'Brien.
Of the 176 local unions with UPS members, 14 affiliates did not show up to a meeting in Washington DC to review the agreement.
The union said the rank and file of UPS Teamsters will have the chance to vote on ratification from August 3 to 22.
(Reporting by Ananta Agarwal in Bengaluru; Editing by Arun Koyyur)