Vice President Leni Robredo (left) with President Rodrigo Duterte (right) on July 1, 2016 in Quezon City. Gregorio B. Dantes Jr./ Pacific Press / LightRocket / Getty Images

President Rodrigo Duterte could have an unlikely opposition leader in the Philippines' legislature: one of his own ministers. Philippine Vice President Leni Robredo told local news outlets on Monday that she was ready to head up a new opposition party. Her comments came a day after she resigned as housing secretary, a position she was appointed to in July by Duterte himself; vice presidents are allowed to take on concurrent posts in cabinet if the president chooses, according to the constitution. "I will continue to fight against things I do not believe in. If being an opposition leader entails that, then I will be an opposition leader," local media quoted Robredo as saying on Monday. The 52-year-old's Liberal Party is currently allied with Duterte's PDP-Laban party in congress. But if the Liberal Party left the alliance, it could become an official opposition party, with Robredo at the helm, politician Teddy Baguilat said, according to local news. Unlike other democracies, candidates for the presidency or vice presidency in the Philippines are elected separately so it's possible for the people in the roles to come from different parties.

The nation currently lacks a strong opposition and the prospect of more powerful resistance to Duterte comes amid fears of growing authoritarianism in his administration. In a statement on Sunday, Robredo said she stepped down due to "major differences in principles and values" with Duterte, and that the "last straw" came on Saturday, when she received a text message from Cabinet Secretary Jun Evasco that instructed her to stop attending cabinet meetings. "Her resignation gives us a strong sense that the president does not like to work with people who criticize him or his agenda," Jean Franco, assistant professor at the University of the Philippines, told CNBC. Franco believes Robredo will be a successful opposition leader mainly due to her untainted public image and charisma. Robredo, a former human rights lawyer, has been a high-profile critic of the president, having called for an investigation into allegations of extrajudicial killings amid the state's five-month old war on drug trafficking. Human Rights Watch estimates the death toll at about 5,000, while police put the number of people killed by officers in self-defense at 2,400, according to a Reuters investigation published this week.

