Political parties cannot come under the RTI as they are not public authorities. According to RTI act the public authorities are those which are formed by constitution, parliament statue or bodies created by notification or order of the appropriate government, such as planning commission, UIDAI etc. Since political parties do not full fill any of the criteria they cannot come under RTI.
It is apprehended that political rivals might file RTI applications with malicious intentions, adversely affecting their political functioning
Political parties are already under the financial accountability radar through the provisions on the Income tax act and Representation of people act. Election commission has placed wide array of information regarding political parties on its websites.