Voters should consider the Workers' Party's (WP) motives for opposing the Non-Constituency MP (NCMP) scheme, said Deputy Prime Minister Heng Swee Keat yesterday.

He also called on the party to make clear if its candidates would accept these seats, which are offered to losing opposition candidates with the highest vote shares.

"If it is really a matter of principle that the Workers' Party is opposing the NCMP system, why have they taken up the NCMP positions all these years?" Mr Heng said in a video message. "Is it really extinction that the Workers' Party fears? Or is the real motive of the Workers' Party to expand, to win more seats in Parliament?"

In 2016, the Constitution was amended to increase the number of NCMP seats from nine to 12. NCMPs have also been given the same voting rights as elected MPs, meaning that they are able to vote on all Bills and motions, including supply Bills, constitutional amendments and motions of confidence.

Pointing to this, Mr Heng said: "The PAP (People's Action Party) is not trying to shut the opposition out of Parliament. We understand that diverse views are important to ensure the best outcomes for Singapore, and Singaporeans value this diversity."

The scheme has emerged as a key issue in this general election, with opposition parties criticising it as a ploy to entice voters to vote for the PAP.

The WP's Dennis Tan, who took up an NCMP seat in 2015, called the scheme a "poisoned chalice", while party chief Pritam Singh has questioned the PAP's "magnanimity" in highlighting the scheme during the hustings.

While WP MPs have taken up the posts in the past, the party has always maintained that the scheme is a ploy by the PAP to dissuade Singaporeans from voting for the opposition. Former party chief Low Thia Khiang compared NCMPs to "duckweed on the water of the pond", to illustrate his view that they are unable to sink roots in a constituency and build up grassroots support.

Mr Singh, when asked earlier if his party would continue to take up NCMP seats, replied: "It's a very speculative question at the moment, but I'm sure you know we will have to address these matters after Polling Day."

In his message yesterday, Mr Heng said the WP's decision to keep mum on whether it will take up NCMP seats is "playing games with voters", who are entitled to know the party's stand.

"They should not be made to think that the Workers' Party will refuse NCMP seats, the opposition risks extinction, and so vote for them," Mr Heng said. "Then after the elections, the WP takes up NCMP seats that they are offered. And in this way, they can have their cake and eat it."

Mr Heng pointed out that the WP has taken "full advantage" of the NCMP scheme from the start, with eight of the 10 NCMPs to date coming from the party. Party chairman Sylvia Lim, he noted, started out as an NCMP in 2006 before becoming an MP in 2011.

Mr Heng said the WP should answer two questions: whether there can be no "opposition wipeout" with the NCMP scheme in place, and whether its candidates will accept if offered seats.

"The WP talks a lot about transparency and accountability. This is what they need to do, to be transparent and accountable to voters."

Asked for his response to Mr Heng's comments that the WP should clarify its stance on the scheme, and if it will take up NCMP seats, Mr Singh said last night that the party's stance is clear.

"I'm quite surprised Mr Heng, of all people, would make that sort of comment. I would invite him to have a look at the Hansard," said Mr Singh, referring to the parliamentary records.

"The NCMP scheme was introduced in 1984, and there's a long history of a position that the Workers' Party has taken on the NCMP scheme," he added. "It's on record. It's in the public domain. And Mr Heng just needs to look at that."

Progress Singapore Party (PSP) chief Tan Cheng Bock, who also opposes the scheme, has said he would decline an NCMP seat if offered one, although other party members could take it up if they wished to do so.

"At least Dr Tan Cheng Bock of PSP has been upfront," Mr Heng said. "But he may have forgotten that in 1984, when the scheme was debated in Parliament, he supported having NCMPs."

Mr Heng rounded up his speech by stressing that opposition and alternative voices in Parliament are guaranteed by the NCMP and Nominated MP schemes.

"By voting the PAP, Singaporeans will give us a strong and clear mandate to form the next government to take Singapore through this crisis and emerge stronger," he said.

"At the same time, you are assured that opposition and alternative voices will continue to be heard in Parliament. Opposition voices will not be wiped out."