Sen. Tim Kaine is demanding that the White House release a secret memo outlining President Donald Trump’s interpretation of his legal basis to wage war.

The Virginia Democrat, a member of the Armed Services and Foreign Relations Committees, sent a letter to Secretary of State Rex Tillerson on Thursday requesting that he hand over the seven-page document drafted last spring.

Kaine’s concern with the memo stems from the president’s unilateral decision last April to strike a Syrian airfield with Tomahawk missiles worth millions of dollars in response to Syrian President Bashar al-Assad using chemical weapons on his own people.

Lawmakers from both parties questioned the president’s constitutional authority to order the strike. Without legal justification for such military actions, lawmakers worry the president could erode congressional authority over military operations.

“The fact that there is a lengthy memo with a more detailed legal justification that has not been shared with Congress, or the American public, is unacceptable,” Kaine wrote in the letter to Tillerson.

“I am also concerned that this legal justification may now become precedent for additional executive unilateral military action, including this week’s U.S. airstrikes in Syria against pro-Assad forces or even an extremely risky ‘bloody nose’ strike against North Korea,” Kaine wrote.

Kaine renewed his request for the memo as reports percolate that the president is considering a “bloody nose” strike on North Korea — which Kaine and others view as unconstitutional — and as U.S. involvement in the Syrian conflict ramps up.

A Freedom of Information Act Request last fall by Protect Democracy, a nonpartisan executive branch watchdog group, yielded the memo’s existence.

The Tomahawk strike on the Syrian base last spring was against a sovereign nation, not a terrorist group. Many watchdog groups and lawmakers said that meant the bombing was not legally covered by the legislation passed soon after the 9/11 terrorist attacks in New York City that granted the president sweeping authority to wage war against terrorist organizations.

“Congress needs to demand the secret Syria memo when the administration is threatening to use force around the world without authority,” Allison Murphy, Protect Democracy’s counsel who also served in President Barack Obama’s counsel office, told NBC News.

“The American people deserve to see” it, she said.

Kaine and GOP Sen. Jeff Flake of Arizona have proposed a new war authorization bill that reflects modern circumstances, particularly in the Middle East.

Leadership in neither chamber has considered a legislative war powers update in the region.