PHILIPPINE senators on Monday asked the Supreme Court to issue jurisprudence on whether the Executive branch can unilaterally end a treaty that the chamber had concurred in.

This comes after President Rodrigo R. Duterte last month ended a two-decade-old military agreement with the US on the deployment of troops for war games.

“We will ask whether an agreement that is very difficult to enter into can be revoked by a simple letter,” Senate President Vicente C. Sotto III, who filed the lawsuit with five other senators, told reporters in a teleconference before the filing.

“In cases like these, the Supreme Court is the Oracle we consult,” he said. The 1987 Constitution is silent on the issue.

Joining him in the lawsuit were Senators Ralph G. Recto, Juan Miguel F. Zubiri, Franklin M. Drilon, Richard J. Gordon and Panfilo M. Lacson.

The senators asked the high court to require Senate concurrence by a vote of two-thirds before the Executive can end a treaty.

“It is a continuing effort of the Senate to define our powers,” Mr. Drilon told reporters separately.

Mr. Duterte on Feb. 11 officially notified the US of his decision to end the visiting forces agreement (VFA) after the US visa of Senator Ronald M. de la Rosa, his former police chief who led his deadly war on drugs, was canceled.

Mr. Duterte’s decision could complicate US military interests in the broader Asia-Pacific region as China’s ambitions rise.

The VFA is important to the overall US-Philippine alliance and sets out rules for US soldiers operating in the Philippines, a former US colony.

Washington has called the relationship “ironclad,” despite Mr. Duterte’s complaints that include allegations of US hypocrisy and ill treatment.

Ending the VFA complicates Washington’s efforts to maintain an Asia-Pacific troop presence amid friction over the presence of US personnel in Japan and South Korea and security concerns about China and North Korea. — Charmaine A. Tadalan