Answer: Tax Imposition on whiskey.
Explanation: Farmers from Pennsylvania used to convert corn crops to affordable whiskey to earn livelihood. When tax was imposed, the farmers were no longer in a position to earn profit from making and selling whiskey which lead to a protest by farmers against this. Another secondary cause was that people in colonies were not happy with the prohibition of whiskey, which was not prohibited explicitly but due to high taxes imposed people from lower social class were not having access to good and expensive whiskey which made them angry.