The CVC, which has carried out a detailed preliminary investigation into the scam in various government departments, will be handing over more documents soon, they said.
The agency will register cases to probe alleged involvement of some Members of Parliament in Rajya Sabha) and central government employees, the sources said.
Lakhs of rupees are said to have been fraudulently claimed from the government through fake Leave Travel Concession (LTC) claims, availed by government officials to get concessional tickets.
The incident had come to light after the vigilance department of Air India(AI) was alerted about the arrest of a man in March this year at the Kolkata airport with 600 blank boarding passes of the airline in his possession.
Smelling a rat and an alleged criminal nexus between air travel agents and government employees, Air India got in touch with the Central Vigilance Commission (CVC) which has now asked the CBI to look into the matter.
One of the cases to be probed is the LTC facility availed on December 13, 2012 when seven tickets of 'Executive Class' were purchased for travel on the Delhi-Kolkata-Port Blair route and back.
The AI in March got a letter from the Rajya Sabha Secretariat asking the airline to conduct an inquiry into this case after it got LTC claims from seven individuals in this regard.