Lawmakers in the Lower House are scheduled to debate the second and third readings of the bill on Thursday and Friday. With the ruling Pheu Thai Party dominating the chamber, Mr Korn conceded the bill would pass, leaving the court as the opposition's best option.
The Democrats will argue in court that the bill breaches the constitution, which states the need for the government to be financially disciplined, he said.
The party has maintained that the borrowing is unnecessary and that with proper planning, long-term infrastructure projects could be financed from the government's regular budget.
"I've told the present finance minister that you were betraying the position because your duty was to keep financial discipline in check," he told a forum at the National Institute of Development Administration, referring to Kittiratt Na-Ranong.
Mr Korn has criticised Mr Kittiratt for his failure to perform this duty by backing projects which could jeopardise the country's financial position.
The Democrat deputy leader raised concern that the infrastructure bill could set a precedent for others to follow if the government wants to seek funds for education and healthcare improvements. Such practices could eventually lead to financial collapse, he warned.
Of the money to be borrowed with the backing of the bill, an estimated 1.2 trillion baht would be used to build a high-speed train network and improve the railway tracks across the country.
The government wants to overhaul the transport system by encouraging travellers to use trains and businesses to use the rail system for more efficient logistics. Logistics costs accounts for 14% of gross domestic product, much higher than in many other countries, and that impairs Thailand's competitive edge, supporters of the government's plan say.
Most projects under the 2-trillion-baht bill will be carried out under the Transport Ministry.
Transport Minister Chadchart Suttipunt in a separate event stressed the need for the country to spend the money for infrastructure improvements, especially the railway system to prepare Thailand for future linkages with other countries when the region becomes a common market at the end of 2015.
Better logistics will lure investors to Thailand and tap the country's geographical advantage as a centre linking other Southeast Asian markets with China, he added.
Mr Chadchart has said benefits from the high-speed trains would include expansion of wealth and economic opportunities out of Bangkok to other areas where the trains reach.
The government plans to build four lines from Bangkok to Chiang Mai, Nong Khai, Rayong and Padang Besar in Sadao district of Songkhla. The projects will be built step by step starting with the lines to Phitsanulok, Nakhon Ratchasima, Rayong and Hua Hin.