The Assembly spent three hours debating the issue before the president, Pornpetch Vichitcholchai, called a break so that opposing legislators could discuss the issue privately and reach a conclusion.
The deadline for the enactment was yesterday and Pornpetch was ensuring the deliberation finished in time.
Legislators later voted 166 to 35, with five abstentions, in favour of the change to the Senate groupings.
The passage was despite the Constitution Drafting Commission (CDC)’s argument that the original 20 professional guilds were more inclusive and that the greater number made it more difficult for bloc voting.
The opponents of the clause, such as NLA member Somchai Sawngkarn, argued that in the groups where there were fewer members, bloc voting would more easily occur.
Somkit Lertpaithoon, chairman of the vetting committee, also said there was overlapping between some of the 20 original groups.
Still, the potential for bloc voting remained a major concern. Somkit said that the Election Commission would have to come up with measures to prevent such fraud.
At the start of deliberations yesterday, Somchai also proposed that the enforcement of the bill be put off by 90 days in accordance with its sister bill on the MPs election.
Pornpetch ordered that the committee review the bill and see whether any more changes were needed to match the MPs election law.
The Assembly did not settle whether or not to delay the enforcement of the bill.
As of press time and after more than eight hours of discussion, the NLA had not started voting on the second reading except for some contentious clauses involving composition of the Senate.
The Constitution requires that the Senate be comprised of 200 members selected from different professional guilds.
In the first five years, however, the Senate would have 250 members handpicked by the ruling National Council for Peace and Order.
The Assembly agreed that the senator candidates be divided into two equal groups, one of independent candidates and the other of those fielded by professional associations.
The proponents said that the division could reduce the risk of bloc voting, while the CDC representatives were concerned it could cause questions of constitutionality.
Another issue of concern included the cross-selection of senators, the CDC’s tool to prevent collusion. The NLA’s law vetting committee proposed dropping it and replacing it with selections from within the groups.