A bill to amend the lottery law would make the lottery vulnerable to corruption and could spark a rise in gambling among low-income people, academics say.
The bill seeks to pave the way for the Government Lottery Office (GLO) to hold additional types of lottery, including online gambling.
The bill would also allow GLO board members to serve longer, renewable terms.
"Thailand now risks plunging into the black hole of [financial] disaster as this draft law is actually a state tactic to make money out of luring poor people into gambling," Monthian Boontan, chairman of a Senate committee looking into changes to the lottery law, said.
The bill, drawn up by the GLO, is likely to be proposed to parliament in April.
"The reason behind this move is that the government is broke," Mr Monthian told a seminar on the GLO bill, held by the committee on Tuesday.
Mr Monthian said three aspects of the bill should be changed.
Firstly, the GLO's board of directors must comprise people from different backgrounds rather than a single group of people, Mr Monthian said.
He said a mix of people and interests on the board would prevent manipulation by politicians.
Secondly, the status of the GLO's board should be changed from a state enterprise to de-emphasise the GLO's mandate to make profits.
Thirdly, the financial management of the GLO must have more transparency.
The bill was originally drafted when the Thaksin Shinawatra government launched the two- and three-digit lottery, Wichian Tansirimongkol, chairman of the political science programme at the National Institute of Development Administration, said.
The two- and three-digit lottery project was shelved after the Supreme Court ruled in 2007 the scheme was illegal, Mr Wichian said.
The current government, however, dusted off the old lottery project and even tried to legalise lottery vending machines, he said.
Mr Wichian added that studies carried out overseas show that access to lottery vending machines makes it more convenient for people to gamble.
"This bill is a hungry tiger," Mr Wichian said. "It wants to swallow everything up."
The government has said that young people will be banned from playing the lottery and lottery vending machines will not be located near schools.
Mr Wichian said those measures will not work in practice.
Wallop Tungkananurak, secretary-general of the Foundation for the Better Life of Children, said the GLO board would be given absolute authority to launch any new forms of lottery.
He also said the move to increase the tenure of GLO board members from two years to renewable three-year terms was misguided and would give the GLO too much power.
"I would recommend that a policy committee be set up to balance the authority of the GLO's board, and that each board member should be allowed to serve for only two terms at most," he said.