The CBI has summoned Bengal minister Sujit Bose for questioning on August 31 in connection with alleged irregularities in appointments at several municipalities across the state, sources in the agency said.

The fire and emergency services minister has been asked to appear before the investigating officer of the case in the Nizam Palace office of the CBI in Calcutta at 11am on Thursday.

This is the first time that a member of chief minister Mamata Banerjee's cabinet has been summoned for interrogation in connection with the CBI probe into alleged irregularities in recruitment at over one dozen municipalities.

The summons to Bose comes within three days of the Supreme Court rejecting the Bengal government's plea to stop the CBI from investigating the case. The government had argued that Calcutta High Court, which had ordered the CBI probe on April 21, had bypassed the state and didn't say why police couldn't investigate the alleged irregularities.

"I have not received the summons till date but have heard about it from my media friends," Bose told this newspaper. "It's strange that without informing the person, the agency chose to inform the media about the summons. I've been in active politics for over four decades and there have been no charges against me so far. This is clearly a political move. Let's see," Bose added.

Senior CBI officials said South Dum Dum was among several municipalities where the agency had conducted searches in June to collect documents. Subsequent scrutiny of the appointment process and examination of allied documents necessitated Bose's interrogation, they said.

Bose was the vice-chairman of the civic body in 2016 around the time that the CBI alleged irregularities in appointments at municipal bodies took place.

The process of appointment in different categories, including cleaning staff to those in Group D, was allegedly orchestrated by Ayan Sil, whom the ED arrested in March for his alleged involvement in irregularities in recruitment in state-aided schools, CBI officials said.

Ayan, now in judicial custody, was also allegedly involved in recruiting close to 5,000 candidates for various permanent posts in around 60 municipalities, the ED said.

The businessman, who owned ABS Infozon that was entrusted with barcoding and evaluating OMR sheets for exams for recruiting candidates in municipalities, would charge separate fees for recruitments in different categories including Group D, driver, cleaner and typist in respective municipalities, the central investigating agency said.

The same company had won the contract of evaluating and putting barcodes on OMR sheets that were used for conducting tests by the School Service Commission for different posts in schools, the ED said.