From June 1, websites which have more than 50,000 unique visitors from Singapore every month and publish at least one local news article a week must obtain an annual licence from the Media Development Authority (MDA).
Websites granted a licence will have to remove "prohibited content" such as articles that undermine "racial or religious harmony" within 24 hours of being notified by the authority, the MDA said in a statement.
"This will place them on a more consistent regulatory framework with traditional news platforms which are already individually licensed," it said.
It has also become a magnet for strident anti-government and anti-foreigner comments posted by readers in reaction to some news stories.
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The MDA said it expected "no change in content standards" since websites must already comply with content restrictions under current regulations.
Licensed websites will have to put up a sum of SgD50,000 (USD 39,500) as a "performance bond" similar to what is required of smaller broadcasters.
Industry sources told AFP the bond can be forfeited if a media company refuses to comply with regulations and MDA directives.
The other nine belong to local media companies Singapore Press Holdings and Mediacorp.
"We are not in a position to respond until we receive the actual licence conditions for review," Alan Soon, the "country ambassador" for Yahoo! Singapore, told AFP when asked for comment.