TBILISI, Georgia — Tens of thousands of opposition supporters are thronging the center of Georgia's capital in a show of strength ahead of Monday's parliamentary election.

An opposition coalition headed by a billionaire businessman is presenting the government of Mikhail Saakashvili with its toughest challenge since he became president nearly nine years ago.

The capital, Tbilisi, long ago turned against Saakashvili, with many people disturbed by what they describe as his authoritarian rule.

Monday's election is being seen as a test of Saakashvili's commitment to democracy as he tries to move the former Soviet republic toward closer integration with the European Union and NATO.

On Saturday, people of all ages converged on the center from four directions on streets closed to traffic for a giant campaign rally on Freedom Square.