They point to how they are synonymous with gerrymandering, gobbling up certain seats and organising others to make them hard for the opposition to win, or even contest.
For instance, when GRCs first came about in 1988, constituencies with a history of high opposition support, such as Anson, disappeared.
In 1996, Eunos GRC, which the PAP won by close margins in two previous elections, was cut up and regrouped into new GRCs.
And Braddell Heights, where Singapore People's Party candidate Sin Kek Tong nearly won a seat in 1991 and planned to contest, was made part of Marine Parade GRC.
Said Hougang MP Low Thia Khiang then: 'Eunos has been traditionally a Workers' Party (WP) stronghold, but it's now split into two GRCs. The intention of the PAP is crystal clear.'
Neither was Mr Low, the WP secretary-general, surprised when Cheng San GRC - which saw a fiery fight in 1997 - was split up in 2001.
'I have said in Parliament before that, maybe, one day, there will be only five GRCs - north, south, east, west and central,' the WP chief said then.
To date, the opposition has not won a single GRC.
WP chairman Sylvia Lim says GRCs raise the bar for opposition parties, while lowering the bar for new PAP candidates.
They also shift the focus of a fight away from the individual to the team and party.
Ms Lim, who became a Non-Constituency MP after her WP team got 44 per cent of the votes in Aljunied GRC in the 2006 General Election, says that contest required a 'considerable' amount of resources.
There is also the feeling that the justification for GRCs seems to have moved away from multiracial representation and economies of scale for town councils, to saying that without them, women or fresh faces cannot be elected.
There are other ways to ensure minority MPs, Ms Lim feels, citing proportional representation for minority candidates in other countries.
'You should want to trust in the wisdom of the voters, that's what democracy is about,' she tells Insight.
To Potong Pasir MP and Singapore People's Party chief Chiam See Tong, voters choose on the basis of merit, not race.
Still, the WP is resolved to win a GRC. At its 50th anniversary celebration last year, Mr Low set his party the target of winning a GRC at the next election.
Ms Lim tells Insight: 'We want to break the GRC barrier, the mindset that we cannot win one.'
RAISING THE BAR
'Eunos has been traditionally a Workers' Party stronghold, but it's now split into two GRCs. The intention of the PAP is crystal clear.'
HOUGANG MP LOW THIA KHIANG, in 1996, when Eunos GRC, which the PAP won by close margins in two previous elections, was cut up and regrouped into new GRCs