From Voices in the Wilderness...
Others directly and publicly refuse to pay part or all of their federal income tax. We do this because roughly half of that tax is used to fund the US war machine.
Tax resistance is the most direct way US citizens can avoid being complicit in this war. If all of us who have written our Congresspersons or taken to the streets also refuse to financially back the war, the decision-makers in Washington have a much harder time ignoring our resistance.
We ask you to consider war tax resistance this tax year, and in the years to come. The best way to stop the war machine is to refuse to fund it.
This is something we have recently considered... divestment from the American government. Here might be a good place to start if you are interested.