Why were the american colonists especially angry with the tea act?

Because they had to pay taxes after the event, the intolerable acts of 1774, and the quartering acts they had to house British soldiers.

This law hurt colonial merchants because they had to pay the tax on the more expensive teas they imported and sold. Colonial merchants worried that the colonists would buy the East India Tea that was less expensive. The colonial merchants would not be able to sell their more expensive teas.