Sen. Tim Kaine, D-Va., is calling for the release of a memo detailing the Trump administration’s interpretation of President Trump's legal authority to wage war, according to a report.

Kaine, who serves on the Senate Armed Services and Foreign Relations committees, sent a letter to Secretary of State Rex Tillerson on Thursday asking for the seven-page document, NBC News reported Friday.

The existence of the memo, drafted last year, was revealed by a Freedom of Information Act request filed by Protect Democracy.

The group sought documents related to the legal rationale for the April missile strikes in Syria authorized by the president. Trump ordered the strikes in response to Syrian President Bashar Assad’s chemical attacks on civilians in the country.

Protect Democracy said because the strikes were against a foreign sovereign country, rather than the Islamic State, there was no legal justification.

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

Kaine said the Trump administration’s recent rhetoric on North Korea, as well as the U.S.’s continued involvement in Syria escalated the need for the memo’s release.

“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 wrote.

This week’s attacks, as well as the missile strikes last year raise "serious questions about our continued presence in Syria," Kaine wrote.

Lawmakers questioned whether the president had the power to launch last year’s strikes and argued the bombing was not covered by an authorization for the use of military force passed by Congress after the Sept. 11 terror attacks.

Kaine and Sen. Jeff Flake, R-Ariz., introduced a new use-of-force authorization against the Islamic State, al Qaeda and the Taliban last year.