A proposed list that specifies offences that can result in suspected criminals being detained without trial worries some lawyers because once detained, they said it would be difficult to challenge the detention in court.
They are also concerned that less severe crimes that fall under the categories in the list may also be dealt with under the controversial Criminal Law (Temporary Provisions) Act.
The Ministry of Home Affairs has, however, said in a statement yesterday that proposed changes to the Act will "restrict the powers of the minister by clarifying the scope of criminal activities under the Act".
It also said that powers under the Act had been used judiciously, and only in cases where prosecution in court was not possible.
For example, when witnesses were unwilling to give court evidence for fear of reprisals.
Yesterday, a Bill introduced in Parliament prescribed, for the first time in more than 60 years, the offences that will come under the scope of the Act. These include organised crime, unlicensed money lending and drug trafficking.
Law don Eugene Tan of Singapore Management University noted that the Act had been wielded with sufficient care in the past.
"I don't doubt the Government's intentions are proper, but there is no guarantee this state of affairs will continue," he said.
Specifying the crimes under the Act could potentially bring less severe crimes under its ambit.
"Once enacted, it could be harder for detainees to challenge the detention even if their alleged crime is not so severe as to merit preventive detention," he added.
Other changes proposed include a provision that says the Home Affairs Minister's decision is final in two aspects: Whether a person is linked to criminal activities, and whether detention is necessary for reasons of public safety, peace and good order.
Lawyer Raphael Louis said: "There is concern in the finality of the decision and whether there will be room for judicial review."
While the changes are necessary to enhance the authorities' powers to tackle crimes affecting public safety, this must be complemented with robust checks and balances by the public prosecutor and the advisory committee that reviews detention and police supervision orders, he added.