MANILA — Four minority lawmakers intend to file a petition before the Supreme Court questioning the extension of martial law in Mindanao until the end of the year.

Albay Rep. Edcel Lagman disclosed this right after Congress decided to grant President Rodrigo Duterte's request to extend military rule in Mindanao until December 31.

Lagman said he has discussed the move with Akbayan Rep. Tom Villarin, Ifugao Rep. Teddy Baguilat, and Magdalo Rep. Gary Alejano, part of what he called the "authentic minority."

Among the grounds the four lawmakers intend to cite in their petition are: the insufficient factual basis for extension, that the extension should not be more than 60 days, and that the coverage cannot be inferred to the whole of Mindanao.

Villarin said the four will secure authentic records of the voting before filing the petition, noting that the recent conclusion of the joint session marks a sad day for democracy and the rule of law.

A total of 261 legislators approved lengthening Proclamation No. 216, while 18 rejected the proposal. The Senate vote yielded a final tally of 16-4, while the Lower House had it 245-14.

• READ: Congress grants Mindanao martial law extension until December

Duterte's request came amid the long-drawn conflict between government troops and Islamic State-linked terrorists in Marawi City.

The ongoing fighting has left at least 578 dead as of Friday night, among them 428 terrorists, 105 government forces and 45 civilians, the military said Saturday.