(Reuters) - The U.S. Supreme Court on Thursday set a date of November 5 for arguments it will hear concerning the legality of Donald Trump's sweeping global tariffs in a major test of one of the Republican president's boldest assertions of executive power that has been central to his economic and trade agenda. 

The justices announced on September 9 that they would take up the case after a lower court ruled that Trump had overstepped his authority in imposing most of his tariffs under a federal law meant for emergencies. 

That ruling stemmed from challenges brought by small businesses and by 12 U.S. states - Arizona, Colorado, Connecticut, Delaware, Illinois, Maine, Minnesota, Nevada, New Mexico, New York, Oregon and Vermont - most of them governed by Democrats. The Supreme Court, which begins its next nine-month term on October 6, also agreed to hear at the same time a separate challenge to Trump's tariffs brought by a family-owned toy company, Learning Resources. 

The tariffs are part of a global trade war instigated by Trump since he returned to the presidency in January that has alienated trading partners, increased volatility in financial markets and fueled global economic uncertainty. 

Trump has made the levies a key foreign policy tool, using them to renegotiate trade deals, extract concessions and exert political pressure on other countries. 

The U.S. Court of Appeals for the Federal Circuit in Washington ruled on August 29 that Trump overreached in invoking a 1977 law known as the International Emergency Economic Powers Act, or IEEPA, to impose the tariffs. The tariffs, however, remain in effect during the appeal to the Supreme Court.

Trump in April invoked IEEPA in imposing tariffs on goods imported from individual countries to address trade deficits, as well as separate tariffs announced in February as economic leverage on China, Canada and Mexico to curb the trafficking of fentanyl and illicit drugs into the U.S. 

The law gives the president power to deal with "an unusual and extraordinary threat" amid a national emergency. It historically had been used for imposing sanctions on enemies or freezing their assets. Prior to Trump, the law had never been used to impose tariffs.