A group of senators will ask the Constitution Court to derail the new public-private partnership (PPP) bill that could enable the government to work with private operators on infrastructure projects without parliament scrutiny.

Appointed senator Paibul Nititawan, who chairs the Senate committee on corruption prevention and government examination, said yesterday he believes the government intends to use the PPP bill to support its projects under the planned 2-trillion-baht infrastructure development borrowing plan.

He disagrees with Section 28 of the bill, which allows the government to guarantee loans for projects in which the state and private sectors are partners.

The loan bill has also not been sufficiently studied, he said.

Consequently, companies that are partners in government projects can use the government's borrowed money without being examined.

That would violate Section 169 of the constitution which requires government spending to be subject to parliament approval, Mr Paibul said.

He also believes the PPP bill violates Section 84 of the constitution, which prohibits the private sector from holding a majority stake in essential public utilities infrastructure.

Mr Paibul said the PPP bill allows the private sector to complete public-private projects with government investment and to wholly own such projects.

The senator warned there could be favouritism between the government and the companies selected as co-developers in these projects.

He said he needed at least 65 MPs _ or 10% _ of all MPs to back the petition.

By yesterday, he had gathered the signatures of nearly 20 senators and was confident he would gain enough support to defeat the bill.

Mr Paibul said that under Section 154 of the constitution, the push to ask the court to reject the PPP bill can go ahead even though it has received parliamentary approval.

It is now pending royal endorsement.

The borrowing bill will be tabled for the cabinet's consideration today before being forwarded to parliament for scrutiny next week.

Mr Paibul noted the opposition Democrat Party had proposed a PPP law but it had required private partners' investment stakes not to exceed 49%.

He also believes the new PPP bill also violates Section 87 of the constitution, which requires the government to promote public participation in politics, economic and social development and the provision of public services.

He said if the PPP bill is passed, the government will be free to proceed with the 2-trillion-baht borrowing bill that he said threatens to damage the nation by worsening existing debts.

If the PPP bill is defeated, the 2-trillion-baht borrowing plan will be stalled because it will lack the support of the PPP bill, the senator said.

The Democrat Party said it will join forces with the senators in the push to block the bill.

Democrat MP Wirat Kalayasiri, who heads the opposition party's legal team, said the PPP bill would allow vested interests to avoid examination by the parliament.

"I think the government plans to use the bill to support borrowing bills," he said.

"We admit we let the bill go because we were not aware and did not know what they were up to," he said.

Meanwhile, Transport Minister Chadchat Sittipunt insisted all the projects can be justified and mechanisms such as reference price adjustments and auditing by outsiders will be put in place to ensure greater transparency.

He said the ministry cannot wait for these infrastructure schemes to be funded by the annual budget process.

Mr Chadchat said that of total infrastructure investments, 80% is earmarked for railways, 14% for roads and the rest would be spent on water transport networks and border checkpoints.

He sought to ease concerns the borrowing would add to the public debt burden, saying these debts would account for only 3% of GDP.

"We should weigh up the benefits of the borrowing, too," he said.

A source in the Transport Ministry said yesterday the details of projects to be funded by the 2-trillion-baht loan would not be included in the ministry's proposal, which is expected to be tabled to the cabinet today.