Some Mennonites practice withholding part of their tax payment as a matter of Christian conscience. They do not believe in paying for war or killing in their name so they don’t pay the portion of their taxes that would normally go to defense or military purposes. They notify the government about what they are doing. In the end the Internal Revenue Service (U.S.) or Canadian Revenue Agency (Canada) still gets the money or the person goes to jail, but some Mennonites who have these convictions feel they are at least making a statement about not wanting their money to pay for making bombs, guns and soldiers. It is a very small percentage of Mennonites who actually put this kind of action into practice.
Read the story of one tax withholder at http://lancasteronline.com/opinion/when-tax-dollars-conflict-with-religious-conviction/article_7585909f-8ed3-528b-8c41-3f6969dd2bf1.html.