Manila - The Philippine vice president said on Sunday that she will resign her Cabinet post, citing "major differences in principles and values" with President Rodrigo Duterte and an unspecified plot to remove her from the vice presidency.Leni Robredo, a human rights lawyer and respected political newcomer, said in a statement that she will tender her resignation on Monday as housing secretary, an appointment made by Duterte, but will stay on in her elected post as vice president.In the Philippines, presidents and vice presidents are separately elected and have often come from rival political parties, like Duterte and Robredo.Hallowed cemetery"I will not allow the vice presidency to be stolen. I will not allow the will of the people to be thwarted," Robredo said without elaborating. "I will continue to serve the Filipino family and fulfill their dream for a better life."Her resignation comes amid a political storm Duterte has faced over his decision to allow the burial of long-dead dictator Ferdinand Marcos in the country's Heroes' Cemetery and a bloody government crackdown against illegal drugs that has alarmed Western governments and human rights watchdogs.Robredo is the second key official to resign from Duterte's administration in less than a week. Maria Serena Diokno resigned as head of the government's historical commission on Tuesday to protest Duterte's decision to allow Marcos' burial in the hallowed cemetery.Diokno has since joined street protests by anti-Marcos groups condemning the burial, which was secretly carried out while left-wing petitioners were preparing to appeal a Supreme Court ruling that upheld the president's decision to authorise the entombment.Robredo cited her opposition to the burial, the drug killings, Duterte's plan to re-impose the death penalty and "sexual attacks against women" among the issues on which she differed with Duterte, who took office on June 30.Impossible to workThe last straw, she said, was when she was notified on Saturday by Cabinet Secretary Leoncio Evasco Jr through a cellphone message about the president's order for Robredo "to desist from attending all Cabinet meetings" starting Monday.Evasco said Duterte decided to bar her from Cabinet meetings because of her "irreconcilable differences" with the Duterte administration.Duterte's move, Robredo said, made it impossible for her to do her work.