An anti-government protester shout slogans outside a business building owned by SC Asset Corp during a rally in Bangkok February 20, 2014. [Photo/Agencies]

BANGKOK - Protesters campaigning for months to oust Thai Prime Minister Yingluck Shinawatra turned their anger on businesses linked to her wealthy family on Thursday, rallying outside the offices of a property developer whose shares fell 5 percent.

Policeman and protester killed in Bangkok clashes   Thai police start to reclaim rally sites, 2 injured

Yingluck's government appears increasingly hemmed in by opponents and the judicial system, lacking the fiscal powers to fund key policies and warned by a court on Wednesday that it cannot use a state of emergency to disperse protesters.

Four protesters and a police officer were killed on Tuesday, in the deadliest clashes since the unrest began in November, when police attempted to reclaim sites near government buildings that have been occupied for weeks.

The protesters are seeking to unseat Yingluck and stamp out what they see as the malign influence of her brother, Thaksin Shinawatra, a self-exiled former premier regarded by many as the real power behind the government.

Around 500 protesters gathered outside the north Bangkok offices of SC Asset Corp, a property developer controlled by the Shinawatra family, waving Thai flags and blowing whistles.

"We will hamper all Shinawatra businesses," protest leader Suthep Thaugsuban told supporters at a Wednesday night rally. "If you love your country, stop using Shinawatra products and do everything you can so that their business fails."

Yingluck was executive chairwoman of the company before being swept to power in a landslide election victory in 2011.

Shares in SC Asset fell 5 percent on Thursday, following a similar fall the previous day. Shares in M-Link Asia Corp , a mobile handset distributor with links to the Shinawatras, have also lost almost 10 percent over the past two days.

Problems continue to mount for Yingluck, who has headed a caretaker government with limited spending powers since calling a snap election in December. Voting on February 2 was disrupted, and it could be months before a new government can be installed.

An anti-corruption agency this week filed charges against her over a soured rice subsidy scheme that has stoked middle-class anger and left hundreds of thousands of farmers, her natural backers, unpaid.

More than 1,000 farmers, many riding in farm trucks, were travelling in convoy towards Bangkok from the central plains, the main rice-growing area, on Thursday.

Chada Thaiseth, a former member of parliament, said he would lead farmers to Bangkok's Suvarnabhumi Airport.

"We are not sure where we will set up camp, but we will not leave the capital until we are paid for every grain of rice sold," Chada told Reuters.

It was unclear whether the farmers intended to protest at the airport, which was blockaded for eight days by royalist, anti-Thaksin "yellow shirts" in 2008.