I found a decent letter template to adapt for my purposes here. Here is the letter I sent in its entirety:
Dear Rep. Taylor:
I am writing to ask you to please oppose H. Res. 888. This resolution attempts to rewrite American history with many demonstrably false assertions, documentation of which can be found at http://tinyurl.com/2b3kvx.
At first glance, this resolution may appear noncontroversial, but please do not be misled. It is a historically inaccurate attempt by the religious right to rewrite American history to promote their agenda.
Unfortunately, I am convinced that there are many people in the country and even some in Congress who would like to turn our great nation into a Christian theocracy. Aside from being filled with inaccuracies about the Founding Fathers and how they arrived at their ideas for our Constitution, this H. Res. 888 is clearly an attempt to establish one religion as the "official" religion of the United States. I am appalled that this is even being considered.
I note with disappointment that you voted for H. Res. 847 (Roll 1143), "Recognizing the importance of Christmas and the Christian faith." I appreciate that you are committed to your own religious beliefs. However, because you are a government official tasked with representing all citizens in your district regardless of their religious belief (or lack thereof), I find it concerning for you and any other members of Congress to express approval of any religion.
I hope that you will oppose H. Res. 888 and that you will not support similarly un-Constitutional bills in the future.
Tags: politics, Congress, religion, activism, church and state, H. Res. 888, atheist, atheist activism