The early settlers in the British colonies were great tea drinkers and Britain was immersed in financial difficulties at the time. In 1767 British Parliament passed the Townshend Acts, a duty (tax) on various products imported by the colonists. This raised quite an uproar in the colonies so the act was repealed in 1770, all except the duty on tea, which was retained to prove that Parliament could raise revenue by taxing without the approval of the colonists. In Boston the duty was circumvented by merchants getting tea which was smuggled by Dutch traders.
Then in 1773 Parliament passed the Tea Act designed to aid the East India Tea Company which was on the verge of bankruptcy with loads of tea they were unable to sell. The Tea Act passed a duty on tea and provided for a monopoly on all tea exported to the colonies. It allowed tea to be shipped only in East India Company ships and consigned tea to its own special agents in the colonies who could undersell the colonial merchant who had bought his tea through a middleman or Dutch smugglers at much higher prices.
Even though Britain was offering tea to the colonies at a cheaper price than they could get it and thought the colonists would favor this, (wrong) it caused quite a rant among the colonists. It would reduce already established colonial merchants to ruin. And it created a monopoly for the East India Company. Much of the ballyhoo was about Britain taxing the colonists without them having a say. (No taxation without representation.)
In New York, Philadelphia, and Charleston, tea agents resigned and canceled orders. In some ports they refused to pay the tax or offload ships. There was a boycott on tea with women becoming leaders in the movement.