(CBS) — United Parcel Service workers and their union have reached a tentative agreement on a five-year contract. If approved, the pact averts what threatened to be the first walkout in decades at the shipping giant.

The deal negotiated with the Teamsters covers 250,000 workers — mostly drivers and package handlers — and includes pay increases. It also lays the groundwork for Sunday deliveries by UPS.

Denis Taylor, co-chairman of the Teamsters’ UPS national negotiating committee, in a statement called the agreement “among the very best ever negotiated for UPS members.”

Starting in August, the deal boosts starting pay for part-time package handlers from $10.35 an hour to $13, with the rate to rise to $15.50 over the next four years. Drivers, who now earn $19 an hour, will see their salary increase to $20.50 later this summer, with their pay climbing to $34.79 an hour in 2022.

Union members will vote next month on the contract. Workers had given the union the go-ahead to call a strike earlier this month, giving the Teamsters leverage in the negotiations.

The last strike by UPS workers in 1997 lasted more than two weeks and disrupted package delivery service around the country.