The US Postal Service is hoping to save as much as $500 million by offering financial incentives to employees who resign or retire before year end.

Eligible employees — members of the American Postal Workers Union or National Postal Mail Handlers Union — will be offered $15,000 to leave. Most of those affected work at mail-processing facilities.

The Postal Service estimates that as many as 30,000 employees might accept the offer, the first since 1992.

Mail volume has been slashed by the recession and a shift to e-mail, prompting the Postal Service to institute a nationwide hiring freeze.

The Postal Service is on track to lose more than $7 billion this fiscal year and is considering other cost-cutting measures such as shuttering some post offices and eliminating Saturday mail delivery.

“Management has been forced to reduce costs, but unfortunately, the cuts have been applied disproportionally to bargaining-unit employees, especially to those in mail processing,” American Postal Workers Union President William Burrus said.

The agreement applies to career full-time employees who retire or leave through voluntary early retirement or voluntary separation. Part-time employees who leave may be eligible for small incentive packages.

About 280,000 employees are eligible for the offer, which is open until Sept. 25.