Maharashtra police received the alert last month, after which their security was upgraded, the official told PTI.
"The names of Nigam, Shelar and Kadam cropped up during interrogation of separatists," the official said, without identifying the organisations that could possibly target them. The official also did not specify the reason for separatists targeting them.
Central agencies sent an advisory to the state Intelligence Department, which passed it on to the Mumbai police, the official said.
Shelar, who heads the Mumbai BJP unit, represents Bandra West seat in the Assembly, while Kadam is an MLA from Ghatkopar West constituency.