Comedian-actor Kapil Sharma, actor Rajpal Yadav, choreographer-director Remo D'Souza, and singer-comedian Sugandha Mishra have received threatening emails from an unidentified individual.
The email warned of severe consequences if their demands were not taken seriously, and stated that failure to respond within the next eight hours could result in actions being taken against them.
"We have been monitoring your recent activities, and we believe it is imperative that we bring a sensitive matter to your attention. This is not a publicity stunt or an attempt to harass you," the email stated.
The message further warned them to treat the email with utmost seriousness and confidentiality.
"Failure to do so may result in severe consequences that could impact your professional and personal life," it read.
Signed by an individual named Bishnu, the email threatened that if there was no response within eight hours, "we will take necessary actions".
Based on the complaints from the celebrities, cases have been registered at Amboli and Oshiwara police stations.
Initial investigations traced the IP address of the email to Pakistan. The police are continuing their investigation into the matter.
This comes days after Bollywood actor Saif Ali Khan was attacked by an intruder at his residence on January 16.
Mumbai Police is closely monitoring the rising security concerns involving prominent personalities in the city.
Notably, politician Baba Siddique was shot dead near his house in the Bandra area of Mumbai in October last year.
The responsibility for the murder was claimed by jailed gangster Lawrence Bishnoi's gang.
Salman Khan, on his part, stepped up his security, even installing bullet-proof windows on his balcony.