Hawaii Congresswoman Tulsi Gabbard has introduced a resolution urging the U.S. to withdraw troops from Syria following a directive from President Donald Trump to secure the country’s oil fields.

The resolution, which calls on Congress to act, is being backed by Just Foreign Policy, a nonpartisan organization that’s been critical of American military intervention abroad and advocates for a foreign policy based on diplomacy and U.S. law.

“President Trump’s deployment of U.S. troops to secure Syrian oil fields that do not belong to us, with talks of welcoming in private oil corporations to take the oil, is unconstitutional and a violation of international law,” Gabbard said in a news release. “Syria’s natural resources belong to the Syrian people.”

Last month Trump ordered the withdrawal of troops from northern Syria, putting at risk the lives of Syria’s ethnic Kurds who have been American allies in the fight against the Islamic State and prompting an overwhelmingly bipartisan vote by the House that condemned Trump’s actions.

Later that month, Trump said he was leaving some troops in Syria to protect the country’s oil fields.

“But we are leaving soldiers to secure the oil. And we may have to fight for the oil,” Trump told reporters Oct. 27. “It’s OK. Maybe somebody else wants the oil, in which case they have a hell of a fight. But there’s massive amounts of oil.”

Trump warned that “somebody else” could claim it. “But either way, we’ll negotiate a deal with whoever is claiming it, if we think it’s fair, or we will militarily stop them very quickly,” he said. “We have tremendous power in that part of the world.”

Trump went on to say that protecting the oil could help the Kurds, and “it can help us because we should be able to take some, also.”

“And what I intend to do, perhaps, is make a deal with an Exxon Mobil or one of our great companies to go in there and do it properly,” said Trump.

Erik Sperling, executive director of Just Foreign Policy, emphasized that under the War Powers Resolution of 1973, the president cannot deploy troops into hostile situations without congressional approval.

Presidents have been finding ways around the law or outright arguing against its constitutionality for years.

“Congress has not authorized troops to ‘secure oil’ in Syria or to participate in hostilities against the governments of Russia, Iran, or Syria,” said Sperling in a statement issued in support of Gabbard’s resolution.

There has been confusion about what exactly the mission is of the approximately 500 troops left in Syria. In contrast to Trump’s statements, military leaders on the ground have said it’s not about securing Syria’s oil, but rather defeating ISIS.

Gabbard, who serves on the House Armed Services Committee, has criticized U.S. military involvement in the Middle East throughout her four terms in Congress and during her campaign for the presidency. She’s been particularly critical of U.S. involvement in Syria, traveling there in 2017 to tour the war-ravaged country and meet with Syrian President Bashar al-Assad.