The U.S. Postal Service announced late Friday it would offer thousands of mail-handlers a $15,000 incentive to retire early, the most recent attempt by the financially-strapped agency to cut costs and stay open for business.

The voluntary offer was extended to roughly 45,000 full-time union employees. It is part of the agency's larger plan to cut its workforce by 150,000 over the next three years and close hundreds of mail-procession centers.

Postal officials said such changes are necessary as a result of the recession and because Americans continue to pay bills and perform other, similar tasks online, instead of doing them through the mail.

Officials said 60 percent of Americans now pay their bills online, compared to just 5 percent in 2000. They also said mail volume peaked at 213 billion in 2006, but has since plummeted by more than 25 percent.

Official also have said the congressional mandate to pre-fund retirement health care benefits has contributed to financial problems.

The agency reportedly lost more than $6 billion in the first two quarters of fiscal 2012.

Eligible employees must decide by July and leave in August. Those who accept the offer will receive the money in two installments â€" December 2012 and December 2013.

A similar, pro-rated deal is being offered to many part-time employees. Handlers perform such tasks as sorting mail in processing centers as well as loading and unloading trucks. 

The National Postal Mail Handlers Union said the deal is "intended to provide a financial cushion and added peace of mind for mail handlers who might be prepared to move on to the next chapter of their lives."

The agency also wanted to close some low-volume rural post offices to save money, but announced earlier this month, amid public outcry, to instead reduce hours of operation.