There are two stages when a Patent Opposition can be filed, one before grant of patent and another after a patent is granted.
India Pre-grant Opposition can be filed after the publication of the patent application in the Patent Journal but before grant of a patent. The Patent Act mandates that a Patent shall not be granted before the expiry of 6 months from the date of publication in the journal. This rule is to ensure that there is a minimum window of 6 months for pre-grant opposition.
India Post –grant Opposition can be filed after the grant of a patent but before the expiry of one year from date of grant.
The Opposition must be filed at the appropriate office along with a statement and evidence in support of the opposition. Patent Oppositions are a highly specialised proceeding and care must be taken in drafting notices.