The opposition Democrat Party will ask the Constitution Court to rule on the legality of the 2.2-trillion-baht borrowing bill as soon as it has passed its third and final reading in the House.
Democrat MP Korn Chatikavanij said the charter court will be asked to intervene because the bill allegedly violates the charter's Section 8, involving fiscal and monetary disciplines.
The bill allows the government to borrow up to 2.2 trillion baht to finance key infrastructure development projects, mostly in the transport sector.
Mr Korn said that seeking loans without going through the normal budget process is unconstitutional.
"I once said the finance minister [Kittiratt Na-Ranong] was betraying the post, which is supposed to keep up with fiscal and monetary disciplines," he said.
"He must be prepared to say no and warn about spending. But it is the finance minister who went ahead with a policy that undermines all those disciplines."
Mr Korn, also a former finance minister, was among the speakers at a forum on the controversial bill, which is set for its second and third readings in the House on Thursday and Friday.
He said if the bill makes it way through the Constitution Court, the government will draw up more borrowing plans.
Mr Korn said he raised a number of objections when the bill was vetted by a House committee. His primary concern was that public debt could jump beyond the threshold of 50% of GDP.
He said an analysis of the cost-effectiveness of an institution indicated the infrastructure investments would take 300 years to break even.
Mr Korn said the figure did not cover interest. If interest was to be factored in, the break-even point would not be achieved for 600 years.
He also questioned the cost effectiveness of high-speed rail link projects that would not link Thailand with any other countries.
The proposed northern high-speed route would end in Chiang Mai, the southern route in Hua Hin and the northeastern route in Nakhon Ratchasima.
Given such designs, Mr Korn said the government should anticipate annual losses of 20 billion to 35 billion baht.
Montri Loktiyanurak, director of the National Institution of Development Administration's Master of Public Administration Special Programme, stressed the importance of the investments in infrastructure projects which would take both time and money.
He said without these investments, the Asean Economic Community would not materialise or bring expected benefits.
Meanwhile, House speaker Somsak Kiatsuranont issued an urgent letter calling the House meeting to discuss the borrowing bill on Thursday and Friday.
A total of 144 MPs have signed up to discuss the bill in the second reading.