How does one file protest on patents that are pending?

Protests by a member of the public against pending applications will be referred to the examiner having charge of the subject matter involved. A protest specifically identifying the application to which the protest is directed will be entered in the application file if: (1) The protest is submitted prior to the publication of the application or the mailing of a notice of allowance under rule 1.311, whichever occurs first; and (2) The protest is either served upon the applicant in accordance with rule 1.248, or filed with the Office in duplicate in the event service is not possible.  For more detailed information on protesting a patent, you may visit our Web site at for the Manual of Patent Examining Procedure (MPEP) Chapter 1900.

USPTO FAQ - Questions and Answers (14AUG2003)