As of 2015, the U.S. Postal Service does not offer free printable shipping labels for customers planning bulk mailings. Although USPS does offer a selection of free shipping supplies, the selection focuses mainly on envelopes and boxes for use with the Priority Mail service.
Major office supply retailers such as Staples offer broad selections of shipping labels. Many of these label products come in large packages that contain between 1,000 and 7,500 labels per box, making them ideal for use in large mailing projects.
Some label products are available from USPS, but the selection includes packages with up to 100 labels, which is relatively narrow as compared with the product selection at office stores.