One issue that cropped up was the scheme's income ceiling.

Nominated MP Cham Hui Fong highlighted the plight of some workers who will not be eligible for the second payment of WIS next month, as their annual incomes exceed the limit due to bigger bonuses received last year.

What is worse, they could face the double whammy of having to return the first payment of WIS received in January, said Ms Cham, the industrial relations director of the National Trades Union Congress (NTUC).

Low-wage workers who qualify for the scheme must be aged at least 35 and earn $1,500 or less a month. This works out to an annual income ceiling of $18,000 or less.

Ms Cham gave an example of a group of workers who received three months' bonus as the company performed well, bumping up their annual income beyond $18,000.

Worried that they may not be eligible for the second payment of WIS, they approached the labour movement for help.

The unionists turned to the Central Provident Fund Board and were astounded when told that these workers may have to refund the first WIS payment, which would be recovered from their bank and CPF accounts.

Ms Cham wondered why these workers had to be 'penalised' for getting good bonuses.

Madam Halimah Yacob (Jurong GRC) also weighed in, saying that the WIS scheme was also not fair to workers who are hardworking and do lots of overtime.

'The harder they work, the faster they hit the limit of $1,500 a month,' said the deputy secretary-general of the NTUC.

The one who is willing to work overtime would then not receive the WIS payments, compared to a worker who does not do so, she said.

Her solution: Do not count overtime pay when deciding on the eligibility of workers for the WIS scheme.

Dr Ahmad Magad (Pasir Ris-Punggol GRC) also proposed some changes to the WIS scheme for lowly paid casual labourers or the self-employed.

Currently, they have to contribute to their Medisave accounts before they can qualify for the WIS scheme. But they do not receive any cash payments for WIS as the entire payout will be channelled to their Medisave.

As most of these workers are cash-strapped, he suggested that they be given a smaller portion of WIS in cash with the rest going to their Medisave accounts.

This will encourage more of them to join the WIS scheme, he said.