The CBI on Sunday served a notice to the wife of TMC leader and Chief Minister Mamata Banerjee's nephew Abhishek Banerjee at his Calcutta residence asking her to join the probe in the coal pilferage case, a development that could further raise the political temperature in poll-bound West Bengal.

The team is likely to question Abhishek Banerjee's wife Rujira Banerjee in connection with the case at her residence, sources said.

The central probe agency had on Friday carried out a fresh round of searches in connection with the case, they said.

The CBI had registered an FIR in November last year against the alleged kingpin of the pilferage racket Manjhi alias Lala, Eastern Coalfield Ltd General Managers Amit Kumar Dhar (of then Kunustoria area now Pandaveswar area) and Jayesh Chandra Rai (Kajor area) besides ECL Chief of Security Tanmay Das, Area Security Inspector, Kunustoria Dhananjay Rai and SSI and security in-charge Kajor area Debashish Mukherjee.

It is alleged that accused Manjhi Lala is involved in the illegal mining and theft of coal from leasehold mines of ECL in Kunustoria and Kajora areas, they said.

"If they think they can use these ploys to intimidate us, they are mistaken. We are not the ones who would ever be cowed down," Abhishek said in a tweet.

"We have full faith in the law of the land," he added.

The assembly elections are due in April-May in West Bengal, where the BJP has launched a vigorous campaign to oust the ruling TMC that had secured consecutive wins in 2011 and 2016 under its leader Mamata Banerjee.

Abhishek Banerjee, who is a Lok Sabha member, wields considerable influence in the party and has been leading the Trinamool Congress' counter-attack.