Bharatiya Janata Party (BJP) spokesperson Nirmala Sitharaman told mediapersons: "Congress is trying to hit at the principal opposition party's prime ministerial candidate. It is a clear case of political vindictiveness coming into play."
Congress leads the United Progressive Alliance government.
Two news portals had claimed last month that former Gujarat home minister Amit Shah had ordered illegal surveillance of a woman at the behest of a "saheb", widely believed to be Gujarat Chief Minister Narendra Modi.
Sitharaman said probe was being done in a matter which was a state subject and where an inquiry was being held under the Commission of Inquiry Act by a retired judge and another member.
She accused the Congress of a "fascist mindset" and said it was a clear case of "getting back" after a crushing defeat in assembly elections in four states.
The union cabinet Thursday approved the setting up of a commission of inquiry into the alleged snooping on a young woman by Gujarat Police.