Hundreds of anti-government protesters forced their way into Thailand's Election Commission building on Monday, raising the stakes in a rolling four-week street rally aimed at toppling the government.

The red-shirted protesters, supporters of ousted Prime Minister Thaksin Shinawatra, have occupied Bangkok's main shopping district for three days in a bid to force Prime Minister Abhisit Vejjajiva to dissolve parliament and call an election.

The "red shirts" have accused the Election Commission of stalling in an investigation of alleged irregularities by Abhisit's ruling Democrat party in a $7.9 million election campaign donation in 2005 from cement manufacturer TPI Polene, which could lead to the party's dissolution.

The storming of the building came hours after the protesters threatened to expand their increasingly confrontational rally, which Bank of Thailand Governor Tarisa Watanagase said could hurt the economy if it continues. Despite warnings they could face a year in jail, tens of thousands remained encamped in an area of upscale department stores and luxury hotels, and said they had no plans to leave, forcing retailers to shut their doors and snarling traffic.

Hundreds tore up fliers ordering them to vacate.

Thai stocks, which have climbed 81 percent over the past 12 months, were about 0.6 percent weaker on concerns over the prolonged protest, bucking gains in most other Asian markets. The baht currency eased about 0.2 percent to 32.38 per dollar in thin trade.

"The impact on retail, hotel and tourism-related sectors seems unavoidable and we should see selling pressure in these sectors," said Chakkrit Charoenmetachai, an analyst with Globlex Securities. Tourism supports about 5 percent of the economy.

Retail and hotel firms fell to three-week lows. Minor International, Thailand's largest hotelier, lost 0.9 percent, hotelier the Erawan Group, which runs a Grand Hyatt franchise, fell 2.5 percent and Central Plaza Hotel dropped 1.9 percent. All four have properties near the protest sites.

Abhisit has called the rally unlawful, but there has been no sign security forces would disperse the mostly rural and working class "red shirts", who say they will not leave until parliament is dissolved.

The government filed a court order on Monday to disperse the crowd and planned to file another to arrest leaders of the rally, which it says violates Thailand's tough Internal Security Act imposed last month to maintain order during the protests.

But the protesters remained defiant. "We won't leave. We have sent our lawyer to the court and will submit an objection immediately if the court issues any order to force us to leave," said Nattawut Saikua, a protest leader.

The "red shirts" now occupy three areas: the shopping district, Phan Fah Bridge in Bangkok's old quarter and the Election Commission's office.

Backed by Thailand's powerful military and royalist establishment, Abhisit said holding a peaceful poll now would be difficult, given the tensions, and he repeated his offer to dissolve parliament in December, a year early.

Analysts say Abhisit would probably lose an election if it were held now, raising investment risks in Southeast Asia's second-biggest economy following a $1.6 billion surge of foreign investment in Thai stocks over the past five weeks on expectations he would survive the showdown.

Economists also caution that continued political turmoil could hit confidence and investment, and might force the central bank to delay an expected interest rate rise.

Raising fears of a blow to retail business, Central World, the second-largest shopping complex in Southeast Asia, and half a dozen other big malls remained shuttered for a second day.

Central World usually attracts 150,000 people a day and generates 45 percent of the earnings of its parent, Central Pattana Pcl, Thailand's top department store operator.

The "red shirts" say Abhisit has no popular mandate and came to power illegitimately, heading a coalition with tacit military support after courts dissolved a pro-Thaksin party that led the previous government. Abhisit says he was voted into office by the same parliament that picked his Thaksin-allied predecessors.