Boston Port Act was a law passed by the British Parliament in 1774. It was one of four laws that were intended to punish the citizens of Boston for their destruction of tea in Boston Harbor on Dec. 16, 1773. The Boston Port Act went into effect on June 1, 1774. It altered the Massachusetts Charter of 1691 to give the British greater control over the colony. The act also closed the port of Boston. The four laws that include the Boston Port Act, together with the Quebec Act, are usually called the Intolerable Acts or the Coercive Acts. They aroused great anger in all the colonies. Many of the colonial legislatures offered to help Massachusetts if it continued to defy England. The Boston Port Act was thus one of the causes of the Revolutionary War in America (1775-1783).