25 CFR § 140.2 - Presidential prohibition.

The President is authorized, whenever in his opinion the public interest may require, to prohibit the introduction of goods, or of any particular articles, into the country belonging to any Indian tribe, and to direct that all licenses to trade with such tribe be revoked, and all applications therefor rejected. No trader shall, so long as such prohibition exists, trade with any Indians of or for said tribe.

(R.S. 2132; 25 U.S.C. 263)