The Constitutional Court has accepted a request by House Speaker Chuan Leekpai to rule on the validity of the budget bill, which is in question after the exposure of proxy voting by a coalition party.
Mr Chuan submitted his request to the court on Friday. The court agreed on Wednesday to clarify the legality of the legislation.
The move followed a call by 90 coalition MPs for the court to end the doubt surrounding the bill.
The bill's status came into question after Democrat Party MP Nipit Intarasombat alleged on Jan 20 that two Bhumjaithai MPs, Chalong Therdwiraong and Natee Ratchakitprakarn, voted in favour of the bill without being present in the House on Jan 10-11.
Mr Chalong admitted he was at a funeral in Phatthalung on Jan 10 when his vote was cast. He said he had left his electronic voting card behind in a House voting machine.
Mr Nipit and Mr Chalong are both politicians in Phatthalung.
Mr Nipit claimed that Ms Natee voted for the bill when she was already on her way to China on voting day.
A video on Channel 7 showed Prim Pooncharoen of Palang Pracharath and Somboon Zarum of Bhumjaithai each inserting more than one card in the voting machines during the budget bill vote.
The legislation sailed through the House in a 253-0 vote on Jan 11, with most of the opposition abstaining, and was passed by the Senate on Jan 21.
The court ordered Mr Chalong, Ms Prim and Mr Somboon to submit their explanations of the proxy voting in writing by Feb 4. The case involving Ms Natee is unclear.
Prime Minister Prayut Chan-o-cha has warned there will be a huge impact on the economy if the 3.2-trillion-baht 2020 fiscal budget is further delayed, but the Fiscal Policy Office said it has 300 billion baht worth of obligation budget funds available for disbursement.