(Reuters) -Parcel giant UPS said on Thursday it will offer voluntary buyouts to its full-time U.S. drivers as part of the largest network reconfiguration in its history - a sweeping overhaul that includes cutting 20,000 jobs and closing 73 facilities.

The Atlanta-based company had in April announced a network reconfiguration plan following a reduction in deliveries for its key customer, Amazon.com, and amid U.S. President Donald Trump's tariffs.

The buyout package is in addition to any retirement benefits such as pension and healthcare, the company said in a statement.

The Teamsters union, which represents about 330,000 workers at UPS, was first to announce the buyout plans, calling them an "illegal violation" of the national contract, under which UPS had committed to create 22,500 more jobs.

"Our members cannot be bought off and we will not allow them to be sold out," said Sean O'Brien, general president of the union.

"UPS needs to live up to the existing contract. They must honor their commitments."

UPS said it intends to adhere to the terms of its contract with the union.