A movement to oust Thaksin Shinawatra swelled last month after his family sold its controlling stake in Shin Corp to Singapore's investment company, Temasek, netting 73.3 billion baht ($1.9 billion).
Critics allege that the sale involved insider trading and tax dodges and complain that key national assets - such as the country's communications satellites - are now in the hands of a foreign government.
On Wednesday, several dozen protesters demonstrated outside Shin Corp's Bangkok headquarters and at the Singaporean embassy, carrying signs saying "Thailand is not for sale" and calling on the Singapore government to halt the deal or face a boycott of Shin products and services.
The Singapore embassy said the government had no influence on the investment decision of a private company.
"The decision for Temasek to withdraw from the deal or not will be made on their own. The Singapore government cannot influence a commercial decision made by a private company," an embassy official said.
"The decision for Temasek to withdraw from the deal or not will be made on their own. The Singapore government cannot influence a commercial decision made by a private company"
Singapore embassy official
Temasek, which is 100%-owned by the Singapore government, is run by Ho Ching, the wife of Lee Hsien Loong, the prime minister.
Temasek has not responded directly to the call by protesters to pull out of the deal but has said it is happy with its investment and was not going to do so.
Tens of thousands of protesters have been holding regular street rallies in Bangkok, the capital, to demand Thaksin's resignation, and they have said they will rally every night until he quits.
Thaksin, who has been accused of widespread abuse of power and corruption, has repeatedly said he will not yield to his critics, but was willing to talk to them.
Thaksin dissolved parliament last month and called for elections on 2 April in the hope of facing down his critics. He has offered to resign if his party fails to secure more than half the votes.
Opposition parties say they will boycott the polls, which Thaksin would almost certainly win because of his strong support in rural areas.
Thaksin was re-elected to a second term last year when his party won 377 of the 500 seats in the House of Representatives. His main defence against critics is that he has a mandate endorsed by 19 million voters.