The note was discovered in one of the toilets of the sprawling ACC building, located around 3.5 km away from Chhatrapati Shivaji International Airport on Sahar Road on Wednesday afternoon.
Immediately, the Central Industrial Security Force, Mumbai police and bomb squads got into action and started evacuating the entire cargo section, and launched a search. It was also decided that people will now be allowed inside only after thorough screening, said officials.
Though the threat note has been received two months in advance, the airport security agencies are not taking any chances.
Top ACC and customs officials were not available for comments in the matter despite repeated attempts by IANS.
In late January 2016, an unknown caller rang the airport and threatened it would be blown up within a fortnight, by February 2016.
Though the security agencies concluded it was a "non-specific threat", all teams were on high alert to prevent any incident.