The Workers' Party (WP) has urged the Government to uphold the ban on all forms of online betting, in a statement posted on its website on Monday night.
It follows an online petition calling for the ban to be upheld, that has gathered nearly 12,000 signatures since Sept 15.
The Straits Times had reported that day that two lottery operators are seeking the green light to legally run online betting services.
The Ministry of Home Affairs said then that it was evaluating applications from Singapore Pools and the Singapore Turf Club.
Online and phone gambling were outlawed under the Remote Gambling Act passed two years ago, but operators can apply to be exempted - and Singapore Pools and the Singapore Turf Club have done so.
The WP opposed the applications, arguing that there are already many legal gambling venues here, including the casinos and hundreds of outlets. Approving the applications would make "virtual betting outlets available in almost every home and mobile device", it said.
Such convenience may encourage Singaporeans to take up the habit and possibly become a gateway to more serious gambling, which has serious social costs, it added.
The WP also said that exempting the operators would undermine the Government's case for banning remote gambling in the first place.
During the debate on the law in Parliament in 2014, the Government had cited concerns about addictive behaviour and easy access to these games, WP said.
"It makes little sense for the Government to close one door on remote gambling in order to 'protect young persons and other vulnerable persons', while opening another door that exposes them to the ills of gambling in their homes."