Mamata Banerjee has set up a commission of inquiry - consisting of retired Calcutta High Court Chief Justice Jyotirmay Bhattacharya and retired Supreme Court Justice MB Lokur - to probe the Pegasus phone-hacking scandal.
Among other points, the judges have been tasked with establishing if there were, in fact, incidents of spying, the role of state or non-state actors if such incidents occurred, and the legality of intercepting communications without judicial oversight, as well as possible violation of the right to privacy.
The commission has been given six months to submit its report.
This comes days after Ms Banerjee's nephew, Trinamool MP and party General Secretary, Abhishek Banerjee appeared on a list of potential surveillance targets.
"We thought the centre would form an inquiry commission, or a court-monitored probe would be ordered to look into this phone-hacking incident. But the centre is sitting idle... so we decided to form a 'commission on inquiry'' to look into the matter," Ms Banerjee said shortly before she left for Delhi.
"... I hope this small step will wake up others. We want it to start as soon as possible. Many people from Bengal have been tapped," she added.
it is a significant move for another reason - it is the first formal inquiry into allegations that an Indian client of Israel's NSO Group used Pegasus to hack hundreds of phones belonging to opposition leaders, journalists, government officials and even a constitutional authority.
Some of these hacks were as recent as July 14 - a phone belonging to Prashant Kishor, who helped Ms Banerjee's Trinamool defeat the BJP in the April-May election. Mr Kishor has been talking to the Congress after leading the Trinamool and Tamil Nadu's DMK to poll wins over the BJP.
The commission has also been asked to establish mechanism of spying (whether by Pegasus or any other means) and who is now in possession of the information collected.
Last week Ms Banerjee, who is travelling to Delhi to unite the opposition against the BJP ahead of the 2024 election, spoke of a "surveillance state" and said it was a "threat" to democracy.
"Three things make democracy - media, judiciary and the Election Commission - and Pegasus has captured all three," she said in a speech shared with several senior opposition leaders.
Calling the Israeli military-grade spyware "dangerous" and "ferocious", Ms Banerjee said she could not even talk to other opposition leaders, as she feared her phone too had been tapped.
In a ferocious attack she said, "Mr Modi, don't mind. I am not attacking you personally. But you, and may be the Home Minister, you are deploying agencies against opposition leaders."
The Trinamool came down heavily on the BJP at the centre, declaring this proved they were afraid of Mr Banerjee and that the party was suffering from "fear-psychosis" after its defeat in Bengal.
Mr Banerjee hit back with a taunting tweet, calling for two minutes' silence for "sore losers".
The centre has rejected calls for a probe of any sort, insisting surveillance of the alleged kind was impossible given existing checks and balances within the country's legal framework.
IT Minister Ashwini Vaishnaw - who, as it turned out, was also on the list of potential targets (albeit before he joined the BJP) told parliament attempts were being made to malign Indian democracy.
Pegasus works by infiltrating phones via 'zero-click' attacks - which do not require interaction from the phone's owner - on or Apple's iMessage or WhatsApp, which is, by some margin, the world's most widely-used instant messaging service, with 400 million users in India alone.