I refer you to the Singapore Constitution which is the sacrosanct law of the land that ICA would have to abide to.
http://statutes.agc.gov.sg/non_vers...pl?&actno=Reved-CONST&date=latest&method=part
Deprivation of citizenship on acquisition of foreign citizenship
134. —(1)
The Government may, by order, deprive a citizen of Singapore of his citizenship if the Government is satisfied that —
(a) he has, while of or over the age of 18 years, at any time after 6th April 1960 acquired by registration, naturalisation or other voluntary and formal act (other than marriage) the citizenship of any country outside Singapore or having so acquired such citizenship before the age of 18 years continues to retain it after that age; or
(b) the citizen, being a woman who is a citizen of Singapore by registration under Article 123 (2), has acquired the citizenship of any country outside Singapore by virtue of her marriage to a person who is not a citizen of Singapore.
(2)
Where the Government has made an order under this Article depriving a citizen of Singapore of his citizenship, he shall cease to be a citizen with effect from the date of the order.
Deprivation of citizenship on exercise of rights of foreign nationals, etc.
135. —(1)
The Government may, by order, deprive a citizen of Singapore of his citizenship if the Government is satisfied that —
(a) he has, while of or over the age of 18 years, at any time after 6th April 1960 voluntarily claimed and exercised any rights (other than any rights in connection with the use of a passport) available to him under the law of any country outside Singapore being rights accorded exclusively to the citizens or nationals of that country;
(b) he has, while of or over the age of 18 years, at any time after 6th April 1960 applied to the authorities of a place outside Singapore for the issue or renewal of a passport or used a passport issued by such authorities as a travel document; or
(c) he is of or over the age of 18 years and has, whether before or after attaining the age of 18 years, been ordinarily resident outside Singapore for a continuous period of 10 years (including any period of residence outside Singapore before 2nd January 1986) and has not at any time —
(i) during that period or thereafter entered Singapore by virtue of a certificate of status or travel document issued by the competent authorities of Singapore; or
(ii) during that period been in the service of the Government or of an international organisation of which Singapore is a member or of such other body or organisation as the President may, by notification in the Gazette, designate.
(2) For the purposes of clause (1) (a), the exercise of a vote in any political election in a place outside Singapore shall be deemed to be the voluntary claim and exercise of a right available under the law of that place.
(3)
Where the Government has made an order under this Article depriving a citizen of Singapore of his citizenship, he shall cease to be a citizen with effect from the date of the order.