Metro Manila (CNN Philippines, February 29) — Like several Cabinet officials, majority of the senators are against the termination of the Visiting Forces Agreement (VFA), Senate President Vicente "Tito" Sotto III said Saturday.

"Majority of us, I believe ha, I'm not sure of the exact number, perhaps 12 or more... are not in favor of abrogation," Sotto said in a media forum.

He agreed with Senator Panfilo "Ping" Lacson that some members of President Rodrigo Duterte's Cabinet have reservations about the abrogation of the country's two-decade-old military agreement with the US.

"I've heard the same concerns from the Cabinet members themselves so I agree with Senator Lacson," Sotto said.

Malacañang on Friday shrugged off Lacson's claim, saying all members of the Cabinet support the President's decision.

Upon Duterte's order on February 11, Foreign Affairs Secretary Tedoro "Teddy Boy" Locsin, Jr. sent the US a notice to terminate the VFA – marking the start of the 180-day period after which it will be effectively scrapped.

The President pushed through with the termination despite Locsin's previous statements in a Senate hearing that the Philippines could lose numerous benefits, including billions of pesos in aid, in junking the VFA. Senators had also passed a resolution calling for a review of the VFA first before deciding on its fate.

Sotto said they are finally taking their case with the Supreme Court on Monday. He said they will file a petition asking the high court to determine whether the Senate's concurrence is needed for the abrogation of a treaty.

The Constitution is silent on this matter, since it only requires Senate concurrence in the ratification of an agreement.

Sotto said he and his colleagues are "optimistic" that the Supreme Court will rule on the senators' favor by August 9, when the VFA will be effectively terminated. Aside from Lacson, Senators Franklin Drilon and Richard Gordon are co-petitioners.

Sotto noted that unlike the petition earlier filed questioning Duterte's unilateral pullout from the International Criminal Court, their new motion is "less controversial."

"We're not naming the ICC, we're not naming the VFA, we're merely saying that the Senate must concur also in any abrogation because we were asked to ratify it, we ratified it," he said.

He also clarified that a win at the Supreme Court does not automatically mean that the Senate will next vote against the President's move to scrap the VFA.

"What we can do is call for a review of the VFA and at the same time the possibility of also asking for a review of the Mutual Defense Treaty," he said.

The VFA, a 1998 agreement between Manila and Washington, legally allows the entry of a large number of American troops, exempting them from passport and visa regulations so they can participate in joint military drills in the Philippines.

EXPLAINER: The Visiting Forces Agreement

Experts say that without the VFA, the Mutual Defense Treaty – which states that the Philippines and the US would come to the defense of the other in case of an attack by a foreign country – would be useless.

Retired Senior Associate Justice Antonio Carpio and former Foreign Affairs Secretary Albert del Rosario on Friday warned that the country's alliance with the US is the only deterrent against Chinese incursions in the West Philippine Sea. The end of the VFA can mark the start of China's more aggressive actions in areas claimed and occupied by the Philippines in the disputed South China Sea, they said.