United Parcel Service Inc. has agreed to end a dual wage system for delivery drivers in its next contract with the International Brotherhood of Teamsters, lowering the chances of a nationwide strike when the current labor agreement expires at the end of July.

The Teamsters announced the tentative pact on Twitter Saturday evening, adding they also persuaded UPS to end a mandatory overtime policy for unscheduled workdays and provide Martin Luther King, Jr. Day as a paid holiday.

In a statement Sunday, UPS spokeswoman Natasha Amadi said the agreement would move current part-time drivers to a Tuesday through Saturday shift to accomodate weekend delivery.

The breakthrough came after a marathon day of negations in Washington, where representatives for both sides scurried in and out of a closely guarded hotel meeting room. The Teamsters-UPS agreement is the largest private-sector collective bargaining agreement in the US—and a linchpin in the supply chain, representing 340,000 drivers.

The Teamsters made it clear from the start they would not agree to any proposal that continued the dual wage tracks established under the last contract. Part-time drivers, the lower tier, make $5 an hour less than full-time drivers, who have a top rate of $39 an hour.

“We had part timers going to work in these warehouses with total disregard for themselves and their families” during the Covid-19 pandemic, Teamsters President Sean O’Brien said during a break Saturday. “We had members that died because they went to work to provide these services to the general public.”