The US will allow the import of hunted ivory from Friday (US time), reversing a Barack Obama-era ban.
The change means heads and tusks from elephants killed between January 2016 and the end of 2018 can be imported from Zimbabwe and Zambia.
The Fish and Wildlife Service Department of the US Government defended the move in an official statement: "Legal, well-regulated sport hunting as part of a sound management program can benefit the conservation of certain species by providing incentives to local communities to conserve the species and by putting much-needed revenue back into conservation."
Conservationists were quick to hit back on social media, with advocacy group The Elephant Project calling the move "reprehensible".
US President Donald Trump even drew fire from his own corner, with Fox News' Laura Ingraham taking to Twitter to attack the President.
"I don't understand how this move by @realDonaldTrump Admin will not INCREASE the gruesome poaching of elephants," she wrote.
Some Twitter users wondered whether the move was mainly to benefit Mr Trump's own sons, who have been criticised in the past for their trophy hunting.
"Great news for @DonaldJTrumpJr," wrote Democrat campaigner Scott Dworkin, alongside an image of Mr Trump's son Donald Trump Jr carrying an elephant's body part.
According to the 2016 Great Elephant Census, the largest wildlife survey in history, African elephant numbers have dropped by about 30 percent from 2007-14.