The Trump administration has put a stop to U.S. purchases of nuclear materials from Iran, a policy that first began under the Obama administration in an attempt to ensure Iran remains in compliance with the landmark nuclear deal, according to U.S. officials who spoke to the Washington Free Beacon.

The Obama administration sparked controversy in Congress and the national security world when it announced in late 2016 that it would spend more than $8 million dollars to purchase Iranian heavy water, a nuclear byproduct, in a bid to keep the Islamic Republic in line with restrictions on these materials imposed under the nuclear agreement.

The Obama administration, in what lawmakers described as a “potentially illegal” taxpayer-funded transaction, paid at least $8.6 million to purchase 32 metric tons of heavy water from Iran. The nuclear byproduct can be used to produce weapons-grade plutonium, which is why restrictions were initially placed on Tehran’s stockpile.

The transaction occurred via an offshore third-party, according to U.S. officials, who made clear at the time that it would engage in further purchases if they were needed to help keep Iran in compliance with the nuclear deal.