Can a protest be filed after a patent application has been published?

Yes, but with restrictions. According to MPEP 1901.06:

“35 U.S.C. 122(c) permits the filing of a protest in an application after the application has been published if there is express written consent of the applicant.“

To file a protest after publication, the following conditions must be met:

• The protest must be accompanied by the written consent of the applicant.
• It must be filed prior to the date the notice of allowance is given or mailed.
• The protest must comply with the requirements of 37 CFR 1.291(b) and (c).

The applicant’s written consent can be specific to a particular protest or can be a blanket consent for certain types of protests.

To learn more:

• protest
• published patent application
• applicant consent