The trademark opposition process is different for every jurisdiction, with a few examples being:
In the EU, a third party can file an opposition within three months of the publication of any given EU trademark application. Any opposition must be filed in writing or using an online form. There is a fee that must be paid before the opposition is considered duly submitted.
Once received, the Notice of Opposition is examined by one of the EU examining attorneys. Only after a thorough assessment are both parties asked to provide supporting documents or any other additional evidence. The opposition can either be justified or rejected based on the final ruling of the EUIPO.
In the UK, the Notice of Opposition can be submitted within two months of the trademark publication in the Trade Marks Journal. The UKIPO advises anyone who intends to file an opposition to consider approaching the owner of the application in question so that they can resolve the issue without IP office proceedings. If an opposition is filed, it must be done using a TM7 - Notice of Opposition and adding the statement of grounds. Once the TM7 is received, it will be checked by the Tribunal to ensure all formalities have been met. Once completed, the applicant will be notified.
In the US, once the application is published in the Official Gazette, any third party can oppose the application within 30 days of the publication date. Upon receiving the Notice of Opposition, the Trademark Trial and Appeal board will inform the applicant, who is required to respond within 40 days (extendable).