Outgoing Philippine President Gloria Macapagal Arroyo swore in a new chief justice Monday whose appointment has been questioned by her apparent successor, sparking fears of a constitutional crisis. Opposition Sen. Benigno Aquino III, who set to become the president-elect in an almost-complete vote count from last week's vote, has vowed not to take his oath of office before newly-appointed Supreme Court Chief Justice Renato Corona, who once served as Arroyo's chief of staff and spokesman. Aquino, who has been leading by more than 5 million votes in a count of election returns by a government-accredited watchdog, has said he preferred to take his oath before a village leader in Tarlac, his northern home province, when Arroyo's term ends on June 30. He said he did not want to take his oath “before a questioned entity.” Arroyo's action has brought the Supreme Court on a possible collision course with Aquino's incoming administration, said Aquino's political adviser, Florencio Abad. “She's really pushing us to the brink of a crisis here,” Abad told the AP. The son of two revered democracy icons, Aquino has questioned Arroyo's appointment of Corona last week, citing constitutional prohibitions on appointments two months before the end of a presidential term. However, a majority of Supreme Court justices - all appointed by Arroyo - ruled in March that the two-month ban does not apply to the position of chief justice. Aquino has ordered his lawyers to study how the Supreme Court ruling, which he deemed unconstitutional, can be challenged, said Abad. Presidential spokesman Gary Olivar said Arroyo's actions were legal and admonished Aquino, asking that he adhere to the constitution by recognizing Corona's authority. Arroyo, who ran successfully for a seat in House of Representatives in the May 10 presidential and local elections, may have been appointing friendly justices to fend off possible legal action against her that Aquino has said his new administration would initiate, Abad said. Aquino has said that he planned to form a commission to investigate allegations of massive corruption and vote-rigging involving Arroyo, who faced several failed opposition impeachment bids, coup attempts and political unrest during her turbulent nine years in office. Aquino has appealed to Arroyo to reconsider her appointment of Corona and leave that decision to him. But Arroyo ignored him. On Monday, Arroyo swore in Corona in a ceremony Monday at the Malacanang presidential palace that was covered only by journalists from state-run news agencies. Arroyo was accused of vote-rigging in 2004 and implicated in several corruption scandals. She denies any wrongdoing. Government corruption has plagued the Philippines for decades, and Aquino's campaign promise to clean it up has endeared him to many in his poverty-wracked Southeast Asian nation, which also has grappled with decades-long Muslim and communist rebellions.