The New York City Bar Association has sent an open letter to President Donald Trump seeking to call his “urgent attention” to various legal restrictions on his power to start a war with North Korea.

“[I] call your urgent attention to the requirements of the U.S. Constitution, federal legislation and international law … and, in particular, to the strict limits our constitution and laws impose on the power of our president to unilaterally commit the nation to war,” Bar Association President John Kiernan wrote. Kiernan noted that the letter was being sent to the White House on behalf of the Bar Association's 25,000 members, who hail from nearly every U.S. state.

The 10-paragraph letter, which was sent last week and was cc'd to cabinet members and U.S. Senate and House leaders, went on to say, “In the absence of an actual or imminent attack on the United States (or in some circumstances on its allies), the president has no authority to commence a war in 'anticipatory self-defense' (sometimes incorrectly called a “preemptive” war) on another nation without prior congressional approval.”

“Although the challenges posed to world peace by the current leadership of North Korea are real,” the letter continued, “bellicose threats and displays of military prowess by that nation do not constitute the type of imminent attack that might justify unilateral presidential action to order a military attack against that country.”

In recent months, President Trump and Kim Jong-Un, North Korea's president, have engaged in increasingly heated personal attacks on each other while touting each country's military might. At the same time, Jong-Un has continued to conduct nuclear tests. The rhetoric and nuclear testing, combined with the perceived unpredictability of both leaders, has spurred concern across continents that war could erupt.

The Bar Association's letter, while not limited to North Korea, appeared to be a reaction to these concerns.

In a “conclusion” section, the letter states that “absent an actual or imminent attack on the U.S., the president is required to seek prior congressional authorization for military action against North Korea.”