Organisers made their own cordon between demonstrators and the security forces in an apparent attempt to ensure there would be no friction with riot police.
Last week, the government unveiled a series of economic reforms, including tax reforms and an increase in VAT rates, to be presented to an international donors' conference in Paris later this month. The government hopes they will bring financial help to an economy struggling after the July-August war with Israel.
The main labour union rejected the tax increases as well as privatisation efforts which it says would take away workers' rights.
Rula Amin, Al Jazeera's correspondent in Beirut, said the reform programme is "supposed to bring investors back to Lebanon, it's supposed to fight corruption ... but there are genuine concerns about the plan. People don't trust the government to fix the economy."
On Monday, the opposition, which includes Shia Muslim Hezbollah as well as Christian and Druze parties, vowed to step up its campaign with daily marches outside ministries and public facilities.
The opposition is calling for early parliamentary elections on the basis that Siniora's cabinet is unconstitutional and not fully representative of all of Lebanon's 18 sects after the resignation of all five of its Shia members.
The five resigned, along with an allied Christian minister, after the government rejected their demands for a veto-wielding share of the cabinet.
The government has said it will continue to confront the opposition and said the latest move was aimed at sabotaging the economy to the benefit of Syria.