On August 29, the U.S. Court of Appeals for the Federal Circuit found that President Trump exceeded his authority to impose tariffs under the provisions of the the 1977 International Emergency Economic Powers Act (IEEPA).

The majority of justices in that case found that the Administration's "interpretation of IEEPA would render it an unconstitutional delegation."

Four dissenting justices argued the President clearly has power under the IEEPA to impose tariffs if he declares an emergency. They concluded that the plaintiffs in the case did not show that the Trump tariffs fail "to meet the preconditions IEEPA sets for the exercise of the presidential authorities that IEEPA grants" and that "IEEPA's language, as confirmed by its history, authorizes tariffs to regulate importation...."

The Supreme Court is now being asked to decide which argument is correct. According to the Associated Press, the Administration is hoping the Court will hear the case in November. 

In the meantime, despite majority in the appeals court ruling against the tariffs, they remain in force for now.

Background: Relevant Text of the IEEPA

Sec. 202. (a) Any authority granted to the President by section 203 may be exercised to deal with any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy, or economy of the United States, if the President declares a national emergency with respect to such threat.

(b) The authorities granted to the President by section 203 may only be exercised to deal with an unusual and extraordinary threat with respect to which a national emergency has been declared for purposes of this title and may not be exercised for any other purpose. Any exercise of such authorities to deal with any new threat shall be based on a new declaration of national emergency which must be with respect to such a threat.

GRANT OF AUTHORITIES

Sec. 203. (a) (1) At the times and to the extent specified in section 202, the President may, under such regulations as he may prescribe, by means of instructions, licenses, or otherwise --

(A) investigate, regulate, or prohibit --

(i) any transactions in foreign exchange,
(ii) transfers of credit or payments between, by, through, or to any banking institution, to the extent that such transfers or payments involve any interest of any foreign country or national thereof,
(iii) the importing or exporting of currency or securities;
and
(B) investigate, regulate, direct and compel, nullify, void, prevent or prohibit, any acquisition holding, withholding, use, transfer, withdrawal, transportation, importation, or exportation of, or dealing in, or exercising any right, power, or privilege with respect to, or transactions involving, any property in which any foreign country or national thereof has any interest;
by any person, or with respect to any property, subject to the jurisdiction of the United States.

Read the full text of the law here: govinfo.gov