Democratic Sen. Tim Kaine of Virginia is demanding that a secret memo that describes President Trump’s interpretation of his legal authority to declare war be released, according to a report.

Kaine, a member of the Armed Services and Foreign Relations committees, urged Secretary of State Rex Tillerson in a letter late Thursday to release the seven-page document, NBC News reported.

The Trump administration has kept the memo under wraps for months, according to the news outlet.

“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, which NBC News obtained.

“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,” he continued.

Kaine has been pushing for the White House to explain the president’s legal rationale for the US bombing campaign in Syria last year in response to President Bashar al-Assad’s chemical attacks against civilians.

The Virginia senator and others worry that actions such as the firing of 59 cruise missiles on the Shayrat air base near Homs in Syria compromises congressional oversight over military action.

Shortly after that strike, several members of Congress called on Trump to justify it under US and international law. Article I of the US Constitution gives Congress the power to declare war.

US Attorney General Jeff Sessions was briefed in April 2017 about the memo, according to a court filing provided by Protect Democracy, a bipartisan group of lawyers, the outlet reported.

Sessions received the briefing so he could know “how to advise the president on future actions,” according to the filing, which cited a DOJ attorney.

The Justice Department declined a request for comment.

There is a new urgency to obtain the secret memo given increasing American involvement in Syria and the president’s rhetoric on North Korea.