Both Murali Pillai and Chee Soon Juan, opponents in the Bukit Batok Single Member Constituency (SMC) electoral contest, have on June 30 spoken out against a "scurrilous" online attack on family.

The attack came to light after Murali, who is running on a People's Action Party (PAP) ticket, posted a video on Facebook addressing the "scurrilous attack against my family".

In his video, Murali referred to a post online about his son.

Murali said the things said about his son has "terribly affected" him.

His son, according to Murali, was involved as a victim in a scandal and also committed offences, and is serving a sentence as the courts have "dealt with all these matters".

He criticised the timing of the attack, which he said "leaves nothing to the imagination".

He also said he was not a perfect father and that families have issues, but such things should "not be brought into politics".

Chee stands with Murali

Chee, who is running as the Singapore Democratic Party's candidate for Bukit Batok SMC, spoke out in support of his political rival.

The veteran opposition politician, who is no stranger to be being smeared and attacked, said this "is not what politics should be".

In a Facebook post on the same day, Chee spoke of Murali's "anguished response".

"I stand with Mr Murali on this," Chee said.

"Politics is about ideas on how we can make our nation better, not personal attacks like this."

Adding to his principled stand, Chee said he may disagree with Murali on his political views, but differences "must not be allowed to degenerate into unseemly smears against the candidates and their families".

Murali edged Chee out in a 2016 by-election by taking 61.2 per cent of votes for the constituency.