Banerjee was virtually cornered in the UPA after she was ditched by Samajwadi Party last month after she and Mulayam Singh sponsored the name of former President Kalam, Prime Minister Manmohan Singh and former West Bengal Governor Rajmohan Gandhi.
Asked why her party has chosen to support Mukherjee with whom she has blown hot and cold in the recent past, Banerjee said, "We took the decision in the interest of the UPA coalition and in greater national interest and keeping in mind the people's interests.
"We are not supporting any individual. But we have no option. It is a tough decision we have taken but not to please anyone. We took the decision reluctantly. The pleasure we would have got is missing in our decision today."
She said, "If we had abstained from voting it would have been a plus for Pranab Mukherjee. If we vote, then also it would be a plus for him. We had no other option."
Asked about her party's stand on the vice-presidential election in which incumbent Hamid Ansari has been named the UPA nominee and BJP leader Jaswant Singh the National Democratic Alliance candidate, Banerjee said, "The party will decide later.
"The vice-president, we will decide later. We are not contesting," she said.
Banerjee said Prime Minister Manmohan Singh contacted her over phone and requested for her party's support for Ansari.
Trinamool Congress earlier proposed name of former West Bengal governor Gopalkrishna Gandhi and former Trinamool Congress MP Krishna Basu as the vice-presidential candidates at the last UPA-II meeting.
