Since the beginning of the 18th century, tea had been regularly imported to the American colonies. It has been estimated American colonists drank approximately 1.2 million pounds of tea each year. Britain realized it could make even more money off of the lucrative tea trade by imposing taxes onto the American colonies. In effect, the cost of British tea became high, and, in response, American colonists began a very lucrative industry of smuggling tea from the Dutch and other European markets. In 1773, the Tea Act was passed and granted the British East India Company a monopoly on tea sales in the American colonies. American colonists were outraged over the tea tax. They believed the Tea Act was a tactic to gain colonial support for the tax already enforced. The direct sale of tea by agents of the British East India Company to the American colonies undercut the business of colonial merchants. The smuggled tea became more expensive than the British East India Company tea. Smugglers like John Hancock and Samuel Adams were trying to protect their economic interests by opposing the Tea Act, and Samuel Adams sold the opposition of British tea to the Patriots on the pretext of the abolishment of human rights by being taxed without representation.

In cities as New York, Philadelphia, and Charleston, tea agents resigned or canceled orders, and merchants refused consignments. In Boston, however, the royal governor Thomas Hutchinson determined to uphold the law and maintained that three arriving ships should be allowed to deposit their cargoes and that appropriate duties should be honoured. On the night of December 16, 1773, a group of about 60 men comprising of  Samuel Adams and the Sons of Liberty encouraged by a large crowd of Bostonians, donned blankets and Indian headdresses, marched to Griffin’s wharf, boarded the ships, and dumped the 342 tea chests, valued at £18,000 (about $1m today), into the water.

In retaliation, Parliament passed the series of punitive measures known in the colonies as the Intolerable Acts, including the Boston Port Bill, which shut off the city’s sea trade pending payment for the destroyed tea. The British government’s efforts to single out Massachusetts for punishment served only to unite the colonies and impel the drift toward war.

Reference:

http://www.bostonteapartyship.com/boston-tea-party-facts

http://www.britannica.com/EBchecked/topic/74947/Boston-Tea-Party

http://www.history.com/topics/american-revolution/boston-tea-party