The U.S. Postal Service probably is wishing it had put "Return to Sender" labels on its white plastic tubs mostly used to deliver bulk mail to businesses. These are the containers that make great storage bins, planters and footrests at the office.

Officially called "flat tubs," the postal containers have largely disappeared over the past two years from the nation's USPS mail equipment service centers, dropping from a population of 20 million tubs to almost 20,000 last fall at a potential replacement cost of nearly $65 million.

With postmasters across the country stressing their need for tubs, the Postal Service started a campaign in September to recover the missing tubs, and now has about 263,000, USPS spokesman Mark Saunders said. "It was just a groundswell of people asking, 'We need these tubs back -- can you help us out?' " he said.

With people and businesses beginning to heed the call and the 3 million temporary cardboard tubs added last fall, the USPS made it through the busy holiday season. But as the Postal Service struggles to get its finances in order, it would like to reclaim its mail tubs so it can avoid multimillion-dollar replacement costs and postage hikes. The USPS has spent almost $4 million on temporary cardboard tubs since September.

As an incentive, the Postal Service is offering amnesty for return of the plastic bins. People can leave them out for postal carriers to take or return them to their local post office.

If that's not incentive enough, the Postal Service points out that the tubs are federal property, with each one carrying a warning that there's a maximum $1,000 fine and three years imprisonment for misuse or theft.

The USPS has used the mail bins for almost 20 years, but their utility has increased since the Postal Service started running mail such as magazines through high-speed automated flat sorting machines over a year ago. The tubs are used to collect the mail at the end of the machines, which have cut sorting costs and increased efficiency, Saunders said.

The tubs appear to have other, unofficial uses.

Last month, an Indiana man was charged with felony theft of two mail tubs, which police caught him using to grow marijuana, according to the Indianapolis Star.

In Tampa last fall, Postmaster Rich Rome put a "bounty" on the containers in the form of steakhouse gift certificates to the top two tub-collecting carriers over a six-day period. One winner brought in 900 tubs in one day, mostly from two businesses, which asked the carrier not to reveal their identity. Overall, the contest brought in more than 8,000 tubs, Rome said.

"It was amazing; I was in shock," Rome said. The two winners chose to have their postal station's supervisors cook breakfast for the whole staff, he said.

The container shortage has forced increased production at Minnesota Diversified Industries, based in St. Paul, which has made the plastic tubs for the Postal Service over the past decade. The nonprofit company, which provides jobs for people with disabilities and produces plastic products only for the USPS, made 6 million of the tubs last fiscal year and plans to produce 7.5 million this year. "It's flattering to make a product that people want to steal," MDI spokeswoman Kathy Kukielka said with a laugh.

The USPS and MDI officials are discussing the idea of selling the plastic tubs to the public at post offices. Until that time, though, the Postal Service is pleading with customers to hand over the tubs.

"Please bring these back in -- no questions asked," Saunders said. "You'll probably get a 'Thank you.' "

"We have faith in our customers that they'll do the right thing and bring them back in," he said.

The U.S. Postal Service is offering amnesty from the $1,000 fine to anyone returning its mail tubs.