The decisions were taken at a meeting of Trinamool parliamentary party meeting here.
Trinamool has 28 members in Parliament, 19 in Lok Sabha and 9 in Rajya Sabha.
Railway Minister Mukul Roy, who is the leader of Trinamool parliamentary party, said the decision to support Ansari has been conveyed by party Chairperson Mamata Banerjee to Prime Minister Manmohan Singh.
Trinamool Chief Whip Sudip Bandopadhyay said the party has decided to oppose any government decision on opening the multibrand retail sector to foreign direct investment and any legislation on forward marketing in commodities and privatization of pension fund.
All the Trinamool MPs were present in the meeting.