Some of the U.S. Postal Service's best customers are employes of the USPS. Especially now.

This week, for example, the American Postal Workers Union will be buying, and using, a lot of 15-cent stamps. More than 250,000 of them, in fact, to mail union election ballots to its members.

Rank-and-file APWU members will get the letters, mark their ballots and send them back -- at an average cost of 20 cents -- by the Sept. 15 deadline.

Two years ago, only 100,000 union members voted. This year the return postage bill is expected to be higher, because rates are up and the ballot packages are fatter because more people are running for office, and more people are expected to vote.

The APWU mailing is one of the biggest from Washington in many years , and one of the largest vote by-mail exercises in the world.

Across town, another union of people who normally deliver the mail is in the process of stuffing post office boxes. The National Association of Letter Carriers is planning to send out nearly 229,000 ballots to its members. They also vote by mail and in their case most of the ballots to members will be delivered by members.

The NALC election two years ago drew a return of 119,000 ballots of more than 200,000 mailed out. This year NALC expects a bigger turnout, and a much bigger postage bill.