In the book Chains, why would the brewing of the tea be an issue for the Colonies at the time?

Chains takes place in the time of the Thirteen English Colonies in the 18th century.  Isabel is owned by the Lockton family, who are Loyalists.  Loyalists were loyal to King George III and to England.  The Rebels, or Patriots, challenged the laws imposed on the Colonies by King George and his government.

The Townshend Revenue Act imposed a tax on tea, which was a popular beverage in the Thirteen Colonies.  Other items were also taxed under the Townshend Revenue Act.  Boycotts caused some of these taxes to be removed by 1770, but the tax on tea remained.  Many Patriots chose to boycott tea in protest of the tax.  The British East India Company had a monopoly on tea sold in the Thirteen Colonies.  The company was heavily in debt, and they benefitted greatly from the tax on tea.  This was one of the main reasons why the tax on tea was not repealed.

Most Loyalists continued to drink tea.  Many Patriots refused to buy or drink it.  This caused tensions between the Loyalists and Patriots.  In Chapter 8 of Chains, Mrs. Lockton, a Loyalist, continues to request "a tray of cookies and a pot of tea upstairs late in the afternoon."  Her Patriot neighbors, however, choose other beverages instead of tea.