Just how Nominated MPs get chosen from the pool of hopefuls has raised some eyebrows.
The names of applicants need not be disclosed - and often have not been. And to some, the selection criteria could be more transparent.
The process begins when a special Select Committee of Parliament comprising eight members sits down and goes through the applicants.
Notably, this committee includes one opposition MP - currently Workers' Party chief Low Thia Khiang - along with PAP office-holders and backbenchers and the Speaker of the House, Madam Halimah Yacob.
The committee decides who goes on a shortlist to be recommended to the President for appointment.
Applicants' names are not disclosed - for example, in 2011 the committee received 50 applications, but revealed the names of only the nine who were eventually selected.
Law don and NMP Eugene Tan last year tabled a question in Parliament asking for the reasoning behind the non-disclosure.
In his response, Leader of the House Ng Eng Hen said a more open process of selection could deter potential candidates uncomfortable with public scrutiny.
And political watcher Zulkifli Baharudin says while a full disclosure of names is "theoretically ideal", NMPs, unlike elected Members of Parliament, are not politicians more exposed to the public.
"I know of NMPs who are not comfortable under the spotlight and that's just the reality of the scheme. More important is what kind of value the NMP can bring to the debate in the House," he says.
Another controversial aspect is how a potential nominee is chosen.
The selection guidelines in the Constitution state those deserving nomination should be "persons who have rendered distinguished public service, or who have brought honour to the Republic, or who have distinguished themselves in the field of arts and letters, culture, the sciences, business, industry, the professions, social or community service or the labour movement".
But what constitutes a distinguished contribution is a grey area.
And the fact that the scheme allows for key sectors to nominate a representative raises questions on the specific roles NMPs should play in the House.
Since 1997, panels were set up to nominate NMPs to represent different interests.
Key groups such as the labour movement, business and the professions were invited to set up panels to put forth candidates for nomination.