The Criminal Law (Temporary Provisions) Act (CLTPA) allows the Minister for Home Affairs, with the consent of the Public Prosecutor, to order the detention of suspected criminals without trial, if he deems it necessary "in the interests of public safety, peace and good order". The orders are up to a year and have to be reviewed annually.
The Act lapses after five years unless it is renewed, which explains why it is "temporary".
In October 2013, the CLTPA was passed in Parliament for the 13th time since it was introduced in 1955 during colonial times to fight organised crime, especially secret societies and gangsterism.
According to last year's Singapore Prison Service annual report, there were 136 detainees as of Dec 31, 2014. Just two were women.
A total of 99 were detained for secret society activity and 22 for illegal moneylending.