Same-day deliveries by letter carriers are going to expand next year.

The United States Postal Service disclosed in a Sept. 19 filing with the Postal Regulatory Commission that it wants to expand its current testing beyond the San Francisco and New York City areas.

It currently has the commission’s approval to test the concept until Dec. 16.

“The Postal Service has determined that it will be necessary to test a variety of metropolitan areas over the next year, in order for the Postal Service to make a final determination on the operational feasibility and desirability” of making such a service a permanent product, the filing said.

Amazon and other retailers have indicated an interest in same-day deliveries in a number of major markets.

The filing did not name the new markets where the Postal Service plans to test.

It asked that the USPS be allowed to continue the project until Dec. 16, 2015.