Workers' Party chief Low Thia Khiang on Wednesday expressed disappointment that Transport Minister Lui Tuck Yew was leaving politics, saying the timing of the decision by the "hardworking minister" has raised questions about his reasons for doing so.
Mr Low added that Mr Lui had done a good job, pointing out that he "goes to the ground to try his best to resolve transport issues''.
He said: "It's a loss to the Cabinet."
He also said that the unexpected announcement of Mr Lui's impending departure from politics has raised speculation about the internal workings of the Cabinet and the Government's handling of a public transport system beset by breakdowns in recent years.
"Was it because of the recent incident of the MRT big breakdown...or is it because he feels he has not been supported by his Cabinet colleagues who is supposed to work as a team to give him enough confidence to stay on and solve the issues?" Mr Low told reporters before he attended his weekly Meet-the-People session.
About 250,000 people were affected when both the North-South as well as the East-West MRT lines broke down in July during the evening peak hours.
He also said he would be "very disappointed'' with the People's Action Party (PAP) if it allows a minister to resign in order to take the heat off public transport issues.
Mr Low noted that Mr Lui's predecessor, Mr Raymond Lim, also left the Cabinet after a stint as Transport Minister and questioned whether the Government needed to fundamentally rethink Singapore's transport model.
"Was it because philosophically I think how they treat transport is not correct and not convincing to the Minister for Transport?" he wondered aloud.
He also suggested that perhaps Mr Lui's morale had been affected after his ward in the soon-to-be-defunct Moulmein-Kallang GRC was "chopped off into pieces and redistributed" into other constituencies.
Mr Low acknowledged that public transport was "a long-term problem" that would "take some time to solve" as the network is heavily used daily.
He was also asked a series of questions on the coming general election, such as whether he feels the PAP is trying to ride the wave of national unity generated by Singapore celebrating 50 years of independence and Singaporeans celebrating the life of founding Prime Minister Lee Kuan Yew, after his death in March.
He declined to comment, saying: "It is better for members of the public (and) the younger generation of Singaporeans to look at what (the PAP) is doing and make their own judgement."
On what he thought of recent comments PAP ministers have made about integrity and town council management, he said: "If they really want to launch an attack,we will respond to them."
Meanwhile, said Mr Low, his party plans to engage younger voters through a younger slate of candidates who will be more savvy on social media, which he admitted to knowing little about.
"I'm not on Facebook," he said, adding that he is not planning to start a Facebook page.
He also said the WP will introduce its candidates soon and that they were "already on the ground".
He said his party would probably not depart from its past practice of revealing only on Nomination Day where its candidates will stand.
He, however, hinted that his party's Aljunied MPs will disclose if they were staying to defend the GRC on Sunday during the sale of the WP's newsletter.
Mr Low was also asked to evaluate the performance of his fellow MPs in the House in the past four years. Recently, various websites have tabulated the attendance of MPs in Parliament.
He said he would leave it to Singaporeans to evaluate them, but added that the role of an MP is not confined to attending Parliament. An MP is also involved in running town councils and serving constituents.
However, he added, MPs should prioritise attending Parliament over other activities.
"That's why you offer yourself to be elected. Parliament is your destination, where you represent the people. So even if you are not slated to speak, at least you (have to be there) to know what happened."