In different countries trademark opposition process is different.
In the US, trademark opposition period is only 30 days, so you have to be pretty fast if you plan to oppose.
In Canada, one has to file a trademark opposition within a 2-month period.
In the UK, an opposition period is 2 months but can be requested to 3 months upon a request made by a party that intends to oppose.
In the European Union, a notice of opposition must be filed within 3 months following the publication.
In Australia, the opposition period is 3 months from the date of publication.
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