 Marshall further noted the oil companies ' arguments that a lease would prevent a governmental body from later imposing a tax would denigrate tribal sovereignty , and that tribal sovereignty was not limited by contractual arrangements . Only the Federal government has the authority to limit the powers of a tribal government , and a non @-@ Indian 's consent is not needed ( by contract or otherwise ) to exercise its sovereignty , to the contrary , the tribe may set conditions and limits on the non @-@ Indian as a matter of right . " To presume that a sovereign forever waives the right to exercise one of its sovereign powers unless it expressly reserves the right to exercise that power in a commercial agreement turns the concept of sovereignty on its head . " 
