The Democratic Progressive Party (DPP) is the first to stake a claim on the Fengshan single-seat constituency, which is making a reappearance on the electoral map after 24 years.
The party has said it will field veteran opposition politician Seow Khee Leng, 75, there in the next general election.
DPP secretary-general Benjamin Pwee, who revealed these plans at a press conference yesterday, said his party is also eyeing the single seats of Potong Pasir and Hong Kah North, as well as Bishan-Toa Payoh and Tanjong Pagar GRCs.
This could set his party on a collision course with other opposition parties.
On Fengshan, which will be carved out from East Coast GRC, Mr Pwee said it was to "fulfil Mr Seow's desire to run there".
The Workers' Party fielded a team in East Coast GRC in the 2006 and 2011 polls. Political observers expect it to do so again, and in newly minted Fengshan.
On a possible clash with the WP, Mr Seow, who was once a WP assistant secretary-general, said: "I have been walking there for more than four to five years and I'm staying around there also."
The veteran, who founded the DPP, contested six general elections under different party banners in the 1970s and 1980s, including as a WP candidate in the former Bedok GRC.
Mr Pwee also dismissed talk of three-corner fights in Potong Pasir, which was held by Singapore People's Party (SPP) chief Chiam See Tong for 27 years before he left to contest in neighbouring Bishan- Toa Payoh GRC in 2011. His wife Lina stood there in 2011 but lost narrowly to the People's Action Party's Mr Sitoh Yih Pin.
Said Mr Pwee, who was an SPP candidate in 2011 but quit the party a year later: "We will put a candidate in Potong Pasir because we believe we can put somebody who is a lot stronger than Mrs Chiam."
But he said he has not decided who to field there, except that the person would be familiar with the area and known to residents.
The DPP central executive committee met yesterday to discuss election plans, a day after the release of the Electoral Boundaries Review Committee report. It is the first opposition party to call a press conference to announce its plans since the boundaries review.
Meanwhile, the National Solidarity Party yesterday said the committee's report was disappointing. NSP acting secretary-general Hazel Poa said in a statement that there was an "absence of clear-cut and objective criteria for any change to electoral boundaries from one general election to the next".
She took issue with the boundaries committee's decision to use a guide of 20,000 to 37,000 electors per MP, among other things, saying the upper limit is almost twice the lower limit, and allows "far too much leeway for subjective manipulation".
The party also questioned whether detailed voting results of the last general election, by polling precincts, were made available to the boundaries committee, and whether these were used in any way in the deliberations on the electoral boundaries.
Typically, the committee is convened by Prime Minister Lee Hsien Loong, who suggests terms of reference for the committee. This time, he had asked it to consider smaller GRCs and reduce the average size of GRCs.