1234, Main Street
Boston, MA 02123
05 April, 2005
<Recipient Address Goes Here>
<time>, you <action taken by the rep>. I am writing to let you know that I am very disappointed and upset at your actions.
<Even though I did not support you in the last election/I supported you in the last election> <I have/and I have> been a supporter of the things you have done since that time. But I cannot put my support behind this.
I think public and I deserve an explanation for your actions. Please respond to this letter in a way that makes it clear that public opinion matters to you. Otherwise, I will almost certainly support a different candidate during the next election.
I look forward to your reply.
encl: <List of enclosed items goes here>