Those nations, in particular, the Seneca Nation of Indians in New York, have vehemently opposed attempts to impose taxes, claiming that they have sovereignty (and thus immunity from taxation) and are protected by existing treaties.

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Order No. 17, a law issued by the Coalition Provisional Authority in Iraq before the Iraqis regained sovereignty in June 2004, gave the companies immunity from Iraqi prosecution.

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"I can go to the Afghan people and argue for immunity for U.S. troops in Afghanistan in a way that Afghan sovereignty will not be compromised, in a way that Afghan law will not be compromised, " he said.

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