Thousands of protesters blocked the main street in Manila's financial district today and called on President Gloria Macapagal Arroyo to step down.
Chanting "Gloria must go", about 2,500 protesters from leftist groups gathered near the monument of Benigno Aquino, a martyred senator and symbol of protest against the late dictator Ferdinand Marcos, waving flags and streamers.
Two Roman Catholic bishops, who were openly critical of the president, and a handful of opposition lawmakers were seen at the protest, which police officers claimed was illegal because there was no permit for the gathering.
Dozens of anti-riot police officers were mobilised to keep the crowd from blocking other already congested roads.
Yesterday, an estimated 50,000 people attended a peaceful prayer rally in Manila's largest park to oppose moves by Ms Arroyo's allies to change the constitution without consulting members of the upper house of Congress.
Catholic bishops had called for yesterday's "Watch and Pray" rally after the House of Representatives tried to push through changes and create a UK-style parliamentary system, a move that critics said was designed to extend Ms Arroyo's powers.