After CBI filed a chargesheet against former Finance Minister P. Chidambaram and his son Karti in the Aircel-Maxis deal, Chidambaram said: "CBI has been pressured to file a chargesheet to support a preposterous allegation," adding that he will contest it vigorously."CBI has been pressured to file a charge sheet to support a preposterous allegation against me and officers with a sterling reputation. The case is now before the court and it will be contested vigorously. I shall make no more public comment," said chidambaram on Twitter.The CBI on Thursday filed a chargesheet against 18 people in Aircel-Maxis deal, including Chidambaram and Karti. Special Judge O.P. Saini has listed the matter for hearing on July 31.The Central Bureau of Investigation (CBI) and the Enforcement Directorate are investigating Karti Chidambaram's alleged role in getting Foreign Investment Promotion Board (FIPB) clearance for the Aircel-Maxis deal in 2006 when his father was the Union Finance Minister."We have filed a chargesheet in Aircel-Maxis case naming 18 persons, including P. Chidambaram and his son Karti Chidambaram," a CBI official said.