A U.S. Postal Service supervisor pleaded guilty to federal charges in California after stealing more than $300,000 worth of checks, collectibles and other goods.

Joivian Tjuana Hayes, 36, agreed to a plea guilty to one count of mail theft and one count of unlawful transfer, possession and use of means of identification, according to the U.S. Attorney’s Office for the Central District of California.

Through Hayes’ work at the Costa Mesa post office, she stole at least 20 checks that were together worth approximately $284,000. Hayes deposited the checks into her own account by forging signatures, the U.S. attorney’s office said.

Another $3,000 in money orders were stolen and deposited by Hayes, according to federal prosecutors.

Investigators also found other valuables, including collectible gold coins and bills. She faces up to 15 years in prison on the top charge and another five for the mail theft charge.

This is at least the third recent incident in which a U.S. Postal Service worker stole valuable mail. A Connecticut-based employee admitted in October to stealing cash and gift cards before resealing envelopes to be put back in other mail streams.

A New York City man pleaded guilty last month to stealing roughly $100,000 worth of sports memorabilia in his work as a mail sorting clerk at a New Jersey facility.

Missing mail should be reported to the Postal Inspector Service, which investigates crimes related to the Postal Service. The office charts missing mail to “identify problem areas and assist Inspectors in tracking down thieves,” according to the Postal Service website.

The Postal Service has a best practices guide for post offices to prevent theft by employees. Some of the advice includes separating out registered mail that requires signatures, preventing mail from being loose outside of full collection bins, and periodically comparing outgoing mail against customer order lists.

Consumers who use the mail are discouraged from mailing checks or cash in favor of money orders. A person cannot stop payment for a money order but it can be replaced or refunded.