The BJP was one of the five political parties targeted by the National Security Agency (NSA), a US intelligence agency, in 2010 according to papers released by The Washington Post, triggering an unusually angry response from New Delhi.
The document stamped July 16, 2010 is part of the court records authorising the NSA to spy on 193 countries, five political parties and other foreign entities such as the World Bank.
"India considers it highly objectionable. And we will certainly raise the matter with the US," senior government sources told HT, a sharp contrast from the muted reaction from the foreign ministry in the past.
Former external affairs minister Salman Khurshid had even dismissed the surveillance as merely "computer analysis".
Reacting to the Post's report based on a tranche of papers leaked by the NSA contractor Edward Snowden, the the External affairs ministry spokesperson said it was "extremely disconcerting that privacy laws in India" were undermined.
The saffron party's IT cell head Arvind Gupta said the issue was a matter of great concern and the party will take it up with an appropriate authority.
"It is matter of concern because it deals with interfering in the democratic process of a sovereign nation," he added.
It seems the authorisation came just four months before President Barack Obama travelled to India. The NSA needs permission from the Foreign Intelligence Surveillance Act (FISA) courts to spy on other entities.
Read: US spy agency bagged court approval to spy on BJP
The BJP was in the opposition when the agency got the nod for spying. It is not clear from these documents if the spying was actually carried out.
The documents have the highest security classification in the US and are marked "TOP SECRET" and "NOFORN" (No Foreign Nationals).
Besides BJP, Pakistan People's Party, Lebanon's Amal party, Egypt's Muslim Brotherhood and National Salvation Front and Venezuela's Bolivaria Continental Coordinator were the other parties on NSA's list.
The NSA is responsible for global monitoring, collection, decoding, translation and analysis of information and data for foreign intelligence and counterintelligence purposes.
India is listed in the document as one of the 193 countries that the NSA was authorised to spy on.
The NSA had also received permission to spy on Asian Development Bank, International Monetary Fund, Organisation of Petroleum Exporting Countries among others.
Documents released earlier show that New Delhi has been identified as one of the 84 cities across the world as a "Special Collection Site" by the NSA.
The Agency also targeted the Indian Embassy in Washington and the Permanent Mission to the UN in New York using a variety of means.
These documents also revealed the NSA had deals with more than 80 private corporations to spy on countries like India.