Shares of mailing and shipping company Stamps.com dropped 10.2 percent on Thursday as the White House aims at revamping the U.S. Postal Service.

The White House wants to return the U.S. Postal System to "a sustainable business model," according to a list circulated by the Trump administration that included several other proposals, including merging the Labor and Education departments.

"The Postal Service's financial difficulties have been an issue raised by past Administrations, GAO, members of both parties in both chambers of Congress, and the Postal Service itself for years," the document said, but did not include any details as to how the revamp would work.

President Donald Trump issued an executive order in April to evaluate the Postal Service and recommend reforms. The move followed criticism by Trump directed at Amazon. On April 3, Trump said the U.S. Postal Service was losing billions every year because of Amazon deliveries.

Stamps.com did not immediately respond to CNBC's request for comment.

The company's stock also had its worst day since Nov. 3, 2017, when it fell 22.6 percent. However, the stock is still up more than 35 percent in 2018 and 73 percent over the past 12 months.