Starhub and M1 plan to take legal action against the telco, following its alleged attempt to discredit them through a smear campaign.
Singtel apparently paid bloggers to speak ill of M1 and Starhub, so as to drive signups for a Singtel telephone plan.
This was done by engaging social media marketing company Gushcloud.
A brief from Gushcloud to its bloggers instructed them to complain about services of Starhub and M1, and push a youth plan by Singtel.
This brief was revealed, following a blog post by Singapore blogger, Xiaxue.
Singtel has denied that its staff wrote the brief, while Gushcloud says it is investigating the matter.