The Townshend Act forbade the [East India] Company frrom selling its goods directly to the colonists. Instead, the EIC had to auction merchandise to middlemen, who then shipped the caragoes to American wholeslaers, who finally sold to local shop owners. In May 1773, Parliament, at the request of the EIC, passed the Tea Act. It imposed no new taxes, but rather allowed the Company, for the first time, to import tea directly from Asia into America. The act cut the price of tea in half and was therefore a boon to colonial consumers.
The middlemen cut out by the act, local smugglers and tea merchants, were not as happy… In November 1773, the East Indiamen Dartmouth, Beaver, and Eleanor entered Boston Harbor with the fisrt loads of the EIC’s tea. The conspirators, probably led by Samuel Adams, were well prepared and highly disciplined: they cleaned the decks when they were finished and took no tea for personal use or later sale.
— William Bernstein, A Splendid Exchange: How Trade Shaped the World
HT: EconTalk
Trade Diversion 